tnttt.com in the foamies forum will describe everything about different foam construction and PMF. How you do your build will depend on where and how you will use your van. I’m prone to get lots of dust, sand and dirt on the floor where I am, plus I fish and hike around water so mud and wet feet hit the floor as well. It stays pretty warm where I’m at but a piece of removable carpet makes clean up easy, I like easy. I don’t do a lot of pavement so road noise isn’t a problem for me. I usually try to build so everything is wedged in but then do a few attachments to existing holes in the wall for easy removal and cleaning. I left a rear vent open once and traveled a dusty dirt road for a couple hours at speed. When I opened the back I had a 1/4” of fine white dust coating every surface. That sort of influenced my future builds! Lol!!! With a new van and being unsure how I was going to use it I would leave everything stock and just use it as a metal tent, maybe a crude platform for a bed, a bucket toilet and a camp box type kitchen to try out layout, function and see what kind of flooring I might need. As the saying goes “results may vary”. If by chance a van didn’t work for you or you needed to sell it you would have a larger market.