I have been thinking about using some Flex Watt heat tape on my bus conversion. Heat tape is mainly used to heat reptile tanks. I have a couple of Ball Pythons and I use a foot of heat tape under each of their tanks to heat a section of their floor to 85 degrees. I've been thinking of all the possibilities for skoolie use! You could heat your floors and your water tanks!
Basically, the tape is 11" wide, and you can get whatever length you want. There are two metal strips, one down each side of the tape, and the heating elements are in between. The tape is only .012" thick! At full power, the tape uses 20 watts per foot. On my snake tanks, I have them hooked up to a rheostat switch that controls the temp. At just over 10 watts, I am able to heat my snake tank floor to 85 degrees through 1/4" thick glass, and an inch of aspen shavings. You can also put a LOT of weight on this stuff without damaging it. I'd imagine that you wouldn't want to hammer nails through it though.
For my bus, I'm planning to strip all of the seats out, pull up the rubber flooring, and lay the tape where the walkways are going to be. I then plan on laying some of that adhesive laminate wood flooring down from the Home Depot. I'll cover the whole floor in that stuff and build on top. I'll connect the heat tape to a rheostat switch and put it on the wall in the kitchen area. I'm not sure of the maximum length that you can get the tape in, but I've seen it in stores on big rolls that were at least 100 feet long. So, say you have 20 feet of walking area in your bus and you want to lay down two strips under your flooring. You'll be running 40 feet of tape at 20 watts max per foot. To heat your floor, you're only running 800 watts.
For the tanks, I'm planning on having a fresh water tank and a black/grey water tank. I'm going to hang them like VonSlatt did on his bus. I've got a lot of inspiration from his website.
I'll hang the tanks using bed rails and the tank will be sitting on a big piece of plywood. I'll use the heat tape between the plywood and the tank. I'll use about three feet of tape per tank. Only 120 watts to heat my tanks! I could keep them heated off the inverter while I'm going down the road too. The tape is flexible so you could wrap it around a round tank as well. It costs about $3.89 per foot. I'll need about 30 feet for my bus floors and tanks (short bus). So, for under $120, I can heat my floors and tanks!
Anyways, it's an idea I have been thinking about. I'll be trying it out on my bus and I'll post lots of pictures and keep you guys updated! Here's what a foot of heat tape looks like: