Responding to Wayfinder...wow, I thought I was geeky about solar vs loads... We went down the path of traditional resistance heaters and decided that the furnace was just more efficient at moving the heat around the basement than one single heater...especially 150 watt. Thus at first we added ducts to the street side weaving the ducts toward the shower and forcing air to the bath. This was a great improvement for when we are on propane. But when not, we are trying heat tracing.... The trick is to attach tracing to EVERY water line since tracing is poor at heating the air but great on contact. Tracing was attached with reflective metal tape every 10 inches to assure direct contact. One electrical outlet was added under the dinette seat nearest the bath to power two runs of tracing ; one to the bath and one to the rear. Access under the bath sink was required to wrap tracing around pipes in the bath. I also added insulation on the outer wall being careful not to obstruct the air flow between the hulls. Two other runs were powered from the ac outlet above the bed on the kitchen side by using a white extension cord neatly adhered to the wall to under the bed. Kitchen drawers were removed to access the water lines there. I found that there was an advantage to the four separate runs vs one or two longer runs as it enabled better coverage of the out side shower lines, the water pump area, and the water intake lines. The water tanks are not protected so it could be argued that this might not be fail safe in super cold temps. I have 3 Bluetooth thermometers that continuously record temps in the hull to help monitor. For context, the trailer homes in eastern WA and travels in Feb through Montana or Nevada where we encounter sub freezing temps... Also, a ball valve shut off was placed in the line ( under the sink) to the toilet as we do not use it with our composting toilet.
