A couple of points on insulation. It is Styrofoam with a capital S. Styrofoam is a brand name of the Dow Chemical Company. It is an extruded polystyrene with a R-5 rating per inch.

I was in the Showhauler factory in May. I do not remember seeing any Styrofoam. They use some beadboard (expanded polystyrene beads) R-4 per inch, in the floor.

The only company using Styrofoam instead of beadboard was in the United Specialities Trendsetters. But they only used it in the floor. They used fiberglass batts in the walls.

I was in 9 different RV, truck conversion factories in May. Just about every time the companies claimed they were using Styrofoam they were actually using beadboard. And when I brought that fact to their attention they did not even know the difference.

Haulmark did use some polyiso but only in a limited area. Most of what they use is beadboard.

There was not one company that I felt did a great job of insulating. Some were better than others. One area in which the truck conversion companies are weak is the enclosing, insulating and heating of the holding tanks.