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I also asked Google Gemini Pro to compare the 5200 Marine Sealant vs methycrylate for this job. It liked both with a nod towards methylcrylate While both are considered "permanent" and high-strength, they are fundamentally different. Methyl methacrylate (MMA) is a structural adhesive that creates a rigid, chemical bond, while 3M 5200 is a polyurethane adhesive sealant that creates a flexible, rubbery bond. For mounting a 40lb Victron MultiPlus in a trailer, MMA is generally superior because it is designed to bear heavy structural loads without "creeping" (sagging over time), whereas 3M 5200 is primarily for sealing hull joints and bedding hardware. Comparison Table: MMA vs. 3M 5200 Plexus MA310 Methacrylate Adhesive$26.37Plexus 4 (29) Opens in a new window 3M 5200 Marine Adhesive Sealant$27.993M Opens in a new window Bond Type Bond Type Structural / Rigid Bond Type Adhesive Sealant / Elastomeric Best For Best For Heavy vertical loads & plastic-to-composite bonding Best For Watertight sealing & shock absorption Cure Time Cure Time 45-60 minutes (Fixture), 24 hours (Full) Cure Time 48 hours (Handling), 5-7 days (Full) See less See more Key Differences for Your Job Load Bearing: The Plexus MA310 is a "toughened" adhesive, meaning it has the stiffness to hold a heavy inverter vertically without any movement. While 3M 5200 is strong, its elastomeric (stretchy) nature means that under a constant 40lb load, the bond can technically "flex" more than you might want for a heavy electronics mount. Adhesion to PVC: MMAs are legendary for their ability to chemically "bite" into PVC. Polyurethanes like 5200 stick well to many plastics, but the bond is mechanical; MMA actually fuses to the PVC surface. Time on the Job: You can mount the MultiPlus onto an MMA-bonded board the next day. With standard 3M 5200, you would need to wait nearly a week for a full structural cure before hanging the weight of the inverter. Recommendation: Stick with the Plexus MA310 for this specific mount. It is the industry standard for bonding mounting boards to fiberglass because it provides a rigid structural connection that won't sag over years of road vibration. If you decide to go with 3M 5200, make sure to get the 3M 5200 Fast Cure version to reduce the wait time to 24 hours. ODORS Since I have chemical sensitivities I also asked about odors....Both eventually emit none with the 5200 taking a bit longer to outgas his is a great question, especially for a confined space like an Oliver trailer. There is a significant difference between how these two adhesives behave during and after the curing process. Summary: Odor Performance Adhesive Odor During Application Odor After Full Cure (24-48 hrs) Plexus MA310 (MMA) Extremely Strong. Sharp, acrid, "fruity" but pungent chemical smell. Zero. Once the chemical reaction finishes, it becomes an inert plastic. 3M 5200 (Polyurethane) Mild. Faint "rubbery" or solvent-like scent. Lingering. Can off-gas a "new car" or rubber smell for weeks. Plexus MA310 (MMA) MMAs are famous for being "stinky" while you are working with them.1 The liquid monomer is very volatile, and you must have all the windows and the roof vent open in your Oliver while applying it. The Good News: Because it cures via a rapid chemical reaction rather than solvent evaporation, the odor disappears almost instantly once it reaches its "peak exotherm" (gets hot and hardens). The Result: By the time you are ready to mount your MultiPlus the next day, there will be no detectable smell in the trailer. 3M 5200 (Polyurethane) Polyurethanes are much more pleasant to work with initially, but they are "slow movers." The "Cure" Trap: 3M 5200 cures by reacting with moisture in the air. This process is very slow (days, not minutes). The Result: Because it stays "alive" for so long, it can continue to emit a faint, rubbery chemical odor for several weeks, especially if the trailer gets hot in the sun. If you are sensitive to "new product" smells, this might bother you in the small cabin of a trailer.

Then just for kicks it suggested where to drill - and it recommended that it be done as Oliver suggested: attach the mounting board to the fiberglass first and then attach the Multiplus 🙂 To mount the Victron MultiPlus 3000 to your PVC board, you'll need to drill for two distinct components: the Wall Mounting Bracket (at the top) and the Bottom Security Screws. Below are the dimensions for the MultiPlus-II 12/3000/120-50 (120V), which is the most common model for North American trailers like the Oliver. 1. Mounting Bracket (The Top "Hook") The MultiPlus hangs on a horizontal metal bracket. Instead of measuring from the floor, it’s easiest to mark the center line on your PVC board first. Bracket Hole Spacing: The bracket has three main holes. The two outer holes are spaced 175 mm (6.89 in) apart. Vertical Position: The bracket sits approximately 7.5 mm (0.3 in) down from the very top edge of the unit’s casing. Drill Bit: Use a 5 mm (3/16 in) or 6 mm (1/4 in) bit for your pilot holes in the PVC. 2. Bottom Security Holes Once the unit is hanging on the bracket, you must secure the bottom to prevent it from "jumping" off the bracket during trailer travel. Width Spacing: The bottom holes are 230 mm (9.05 in) apart. Vertical Distance (Drop): From the top mounting holes (on the bracket) down to the bottom security holes is 478 mm (18.82 in). Total Unit Height: The total height of the MultiPlus-II casing is 506 mm (19.92 in). Pre-Drilling Guide for your PVC Board Measurement Metric Imperial (Decimal) Top Bracket Spacing (Horizontal) 175 mm 6.89 in Bottom Hole Spacing (Horizontal) 230 mm 9.06 in Vertical Span (Top Holes to Bottom) 478 mm 18.82 in Total Unit Casing Height 506 mm 19.92 in Total Unit Casing Width 275 mm 10.83 in 💡 Pro-Tips for the Oliver Trailer Install Pre-Mount the Bracket: Do not glue the PVC board with the MultiPlus attached. Glue the board first, let it cure for 24 hours, then screw the bracket into the PVC. Screw Choice: Since you are screwing into PVC board (which is softer than wood), use coarse-thread stainless steel screws (e.g., #10 or #12). Do not use fine-thread machine screws unless you are using heat-set inserts or T-nuts behind the board. Pilot Holes: Always drill a pilot hole in PVC. If you drive a large screw into solid PVC without a pilot, the board can "mushroom" or even crack under the pressure. The "Air Gap": Victron requires 10 cm (approx 4 in) of clearance above and below the unit for cooling. Ensure your PVC board placement accounts for this airflow in the Oliver’s compartment.

Bonding Requirements This is strong stuff! To calculate the bonding requirements for your Victron MultiPlus 3000 (roughly 42 lbs), we need to look at the "Shear Strength" of the adhesive—this is the force required to slide the board down the wall. 1. The Math: Safety Factors The Plexus MA310 has a lap shear strength of approximately 3,000 to 3,500 psi. Even if we use a massive safety factor for the vibration of a moving trailer (e.g., a 10x safety factor), the adhesive is incredibly over-engineered for this load: Load: 42 lbs. Bond Strength: ~3,000 lbs per single square inch. Required Surface Area: Theoretically, less than 1 square inch would hold the unit static. However, the real challenge isn't the weight; it's the peel force (the unit pulling away from the wall) and the flexing of the PVC board vs. the fiberglass. 2. Recommended Adhesive Coverage For a Victron MultiPlus (approx. 11" x 23" for the MultiPlus-II), you should use a "Picture Frame" bead pattern with an additional "X" through the center on your PVC board. Bead Size: Aim for a 1/4" to 3/8" bead. Quantity Needed: One 400ml cartridge of Plexus MA310 will be more than enough. A standard 50ml "hobby" size will likely be too small to cover the necessary surface area for a large backing board. Bond Line Thickness: MMAs work best with a gap of 0.03" to 0.125". Do not press the board so hard against the fiberglass that you squeeze all the glue out. Use small 1mm spacers (like toothpicks or plastic shims) at the corners to maintain a "cushion" of adhesive. 3. Why This "Overkill" is Necessary While 1 square inch could hold the weight, you want the PVC board to be at least 2" wider and taller than the Victron unit for two reasons: Load Distribution: It spreads the 40lb load across a larger section of the fiberglass hull, preventing the fiberglass itself from flexing or spider-cracking. Heat Dissipation: The MultiPlus gets hot. A larger PVC board acts as a thermal break between the unit and the trailer wall. Summary Checklist for the Install Step Detail PVC Board Size Approx. 14" x 25" (for a MultiPlus-II 3000). Surface Prep Sand fiberglass with 80-grit until matte; wipe with Isopropyl Alcohol. Application Apply a thick perimeter bead and an "X" in the middle. Setting Time Clamp or prop in place for 45–60 minutes before removing support. Full Cure Wait 24 hours before bolting the heavy Victron unit to the board. Pro Tip: Because Plexus MA310 cures via a chemical reaction, it generates heat (exotherm). If you apply it very thick (over 1/2"), it can get hot enough to slightly warp thin PVC. Stick to the 1/4" bead for a perfect bond.

He's probably correct....:)

Thanks! It got down to 12 degrees when I got stuck in Mammoth. Luckily the lead acid batteries hung in there. I guess I have some extra insurance, now.

I asked Oliver how they do it. They use a methacrylate adhesive to bond a 3/4" thick PVC mounting board to the fiberglass. He said I could score the mounting board but that the adhesive is very strong. Once the adhesive is dried, THEN they install the inverter to the board with screws. I mentioned that the Multiplus has feet on it and I couldn't figure out how to mount the Multiplus to a board with those feet. (I later realized I could have cut the board short but I suppose that would have affected ventilation under the Multiplus (?)). He actually looked up the Multiplus and found that a hook and 2 holes are provided at the back of the casing for wall mounting. (They recommend mounting to concrete/masonry - I'm not surprised, this thing is a monster) and say vertical mounting is best for ventilation) I then asked Google Gemini Pro if it recommended a specific type of methacrylate adhesive for this specifc job. This is what it said: When mounting a heavy piece of equipment like a Victron MultiPlus 3000 (which weighs roughly 40 lbs) to the fiberglass wall of an Oliver trailer, the choice of Methyl Methacrylate (MMA) is critical. Because trailers experience significant vibration and road shock, you need an adhesive that balances high shear strength with impact resistance. Top Recommended Methacrylate Adhesives For bonding PVC board to Fiberglass (FRP/Gelcoat), the industry standards are typically found in the marine and transportation sectors: Plexus MA310 (The "Gold Standard"): Why it's better: It is specifically engineered for structural bonding of thermoplastics (like PVC) to composites (fiberglass). It offers a medium cure time (15-18 mins), giving you enough time to align the heavy PVC board before it sets. Strength: It reaches 3,000+ psi and is known for "substrate failure"—meaning the PVC or fiberglass will usually break before the glue does (!!). Modern technology.... Plexus MA560-1 (For Large Surface Areas): Why it's better: If you are bonding a very large PVC board, MA310 might set too fast. MA560-1 has a much longer working time (55-70 mins) and is designed for "thick" bond lines (up to 1 inch). It is highly thixotropic (won't sag), which is perfect for vertical trailer walls. SCIGRIP SG230: Why it's better: This is the primary competitor to Plexus. It is often cited for its excellent "toughness" and ability to handle the thermal expansion differences between PVC and fiberglass, which can be an issue in varying climates. Comparison for Your Specific Use Case Adhesive Working Time Best Feature for MultiPlus Plexus MA310 15–18 mins High stiffness; ideal for heavy vertical loads. Plexus MA560-1 55–70 mins Excellent for large boards or thick gaps. SCIGRIP SG300 10–15 mins Very fast "green strength" (holds weight quickly). Export to Sheets Critical Installation Tips Since you are mounting a Victron MultiPlus, which generates heat and internal vibration (transformer hum), keep these factors in mind: Thermal Expansion: PVC and fiberglass expand at different rates. Using a "toughened" MMA (like those listed above) is essential because it remains slightly flexible enough to absorb that stress without cracking. Surface Prep: While MMAs are "primerless," you should still scuff the fiberglass gelcoat with 80-grit sandpaper and wipe both surfaces with Isopropyl Alcohol or Acetone to ensure no wax or mold-release agents remain. Mechanical Backup: Even with a structural adhesive, many Oliver owners prefer a "belt and suspenders" approach. Consider using the adhesive for the primary bond but adding a few well-placed stainless steel bolts through the hull (if possible) or into the aluminum frame for peace of mind. Would you like me to look into the specific weight-bearing calculations for a certain size of PVC board to see how much adhesive you'll need? How to use Plexus 400ml cartridges This video provides a deep dive into using Plexus structural adhesives in marine environments, explaining why they outperform other bonding methods for composites like fiberglass. Why Plexus Adhesives Outperform Putty & Wet Layup | Marine Bonding Deep Dive Chemical Concepts · 156 views

I talked to Randy at Inverter Sales - he recommended, if I got it right, mounting the unit to a board (HDPE/Plywood/?), scoring the board (with a skill saw/chisel/sandpaper -but go deep if using sandpaper), then using 5200 Marine adhesive to attach it to the fiberglass. Use sticks or tape to wedge the unit against the fiberglass so that it adheres.

Thanks. Finding out how to hang this thing has been my big question.

It's had two owners before me. I looked everywhere for it and the former owner told me when he bought it it was not there. Strange, indeed.

How to keep the inverter/charger wedged against the fiberglass so that it seals was my next question. What did you use to do that?

Can you say more about how the 3000 W inverter charger was secured? I just picked mine up and I was shocked at how heavy it is. Was it through bolted to the fiberglass with a backing plate or was it secured some other way?

It’s really incredible since it came with just about everything else (I bought it used) but yes the build sheet does not show a charger and the outlets don’t work.

I'm using ChatGPT and Gemini Pro to help build my system including adding an inverter/charger which my Oliver, for some reaons, did not come with. I downloaded the pictures to ChatGPT and asked it what it thought -for what it's worth - it liked the install 🙂

As always GJ - thanks for your sage advice. Leaning towards the self-heaters if just because its easier (lol)

Thanks for the warmer idea!