We store our trailer 1.5 hr from our house in a barn that has no electricity. I check on the trailer every 2-3 weeks when we are not traveling with it. The parasitic drain was concerning. I built a battery cutoff switch to easily disconnect the batteries during storage. My build consisted of a Harbor Freight switch, Harbor freight terminals, a plastic electrical box, 18" of 4# wire, a couple grommets and some command strips to hold the box in position. We currently only have 2 batteries so the switch box mounts easily behind them. I may want to rig up something nicer later but this is fitting the bill so far for $20. Build time was about an hour including crimping and soldering the terminals.