Airstream use to do that way back in the day, but I think the lawyers made short order of that with lawsuits due to folks not conforming to codes, etc.
I agree though, it'd be cool to have a shell to play with....but with costs being what they are with the cost of goods going sky high due to transportation costs, the shell could be a pretty penny.
I too loved some of the interior features and material selections they used.
The 19' 75th is WAY out of my budget range, but someone on the forum pointed out the guy to designed them and me a one or two others bought the outdoor screen guard. I installed it about a week ago. It's about as close as I'll come to getting the whole thing.