I suppose if you knew how to specify what you wanted you could have the home body built to your spec and then mount it to your frame. Seems like even the basic showhauler frame could be built by many other shops if they had a good plan to work from. I am having a hard time deciding if I want just a tow vehicle with a lounge or motorhome that tows a car trailer. I have a lot of ideas. I think with some space and a little help, I could build a pretty good shell. Guys have done it. I think your post should get more responses.
2k PSD F-250 dually conversion
Alpenlite Durango Camper
Thinking Retro - Needlenose Pete KW or early Freightliner Conventional - Pre Diamler Benz