Just starting to build out my 159" and appreciate all the great info I have found on this forum. My van currently being built here in Florida will be driven out to Colorado in about a month to be used as a mobile office, material hauler and RV to build a house in Mt Crested Butte at 9,500 ft. Once the house is built it will be finished and used as an RV. I want it to be warm so insulation is a priority. The only Polyiso in 1.5" that I could find was for roofing. So far I have templated the floor using a roll of paper and have fitted the iso onto the floor. I now plan to put a 3/4" layer of plywood down that I will route grooves to lay in 1/2 pex tubing and aluminum heat transfer plates. Im going to use an Espar hydronic III D5E to heat the floor and hot water. The plan is to use Glycol in the floor and a heat exchanger to heat a small tank of water. I wish I could of found the aluminum backed polyiso in 1.5" because this material has fiberglass in paper covering that is no fun to work with. The remainder of the van will be insulated with 3.5" wool batts. I was going to use the polyiso for the walls too but think the wool will be easier to install and will accommodate wiring and plumbing easier and will also be a much greener option with no outgassing. Not nearly as cheap though. It cost $625 for 360 ft2. Another thing I'm doing is not cutting the polyiso too close to the walls since I think this may cause squeaking. Im leaving about a half inch all around that Ill fill with wool. Now if I can get the ichy fiberglass off me. Horrible stuff!