I'm always amazed at the prices they ask for the class B vans, just crazy. For something I'd be able maybe to put up for one night in. Certainly not any extended time. But as anything else there's a market for certain people.
Many of the high end diesel pusher use the same materials, even across lower to higher product offerings with the same mfg. More horsepower ( Motorhomes), accessories and bling drive it up from there.
I believe it's Tiffin who's slides I've seen which are molded one piece design.
The Novi MI show is in a few weeks. We plan to go even though we purchased a motorhome last summer. I like looking at the retro trailers and Motorhomes.
We had a number of fifth wheels over the years. One thing that made me turn and exit them in the shows was the spongy floor you mentioned. I was surprised how many we experience that had them.
https://www.gmcconversionvans.com/classb/airstream-interstate/