The foil insulation that you describe sounds similar to the Reflectix brand. This is the type of insulation that Showhauler uses in their units.

I have used Reflectix in some house insulation situations. But I am not sure if I want that as the only insulation.

My requirements for insulation are different than most people's due to where I live. I live at 9,100 feet with regular trips on roads at 11,000 feet to 12,000 feet elevations. We have already had night time lows of 30 degrees. But we are still getting daytime highs of 70 degrees. Depending on the weather we might have snow skiing in 6 to 7 weeks.