Thanks Harvey for your very thoughtful and detailed answer. I need to work on doing shorter posts! But it put a lot of information together that I think will be useful to many including me. It all made sense when you said that early frame separation due to unanticipated full-holding tank driving is what people mostly mean when they talk about it, but of course, the same structural conditions exist in any of them since they're designed fairly close to tolerance. I just looked and mine has 4" frame members, but it doesn't have any holding tanks. Jill totally busted me on the waterbed and projection TV system; guess I better think again on that, and just do a nice restoration to original in this one. If I got that gutted '48 Whirlwind though I don't know if I could resist all the fancy stuff (red leather tuck-n-roll dinette booth, clothes processor, Japanese soaking tub, sound system, solar radiant floor heat, solar panels and batteries, maybe a removable roof deck made with industrial grating ... AND of course the Harley). I guess the space program has come up with all kinds of new sheet-type materials, but have they invented anything structural that's stronger, lighter, rust-free and as flexible as steel? I mean there would be nothing stopping doing a complete frame replacement with some fancy, lighter and stronger material and still have it be the nimble package that it was designed to be, right? Nothing except money, of course, but this is my fantasy and they're meant to be elaborate. In the real world I'm more attracted to the idea of living in as small and efficient a space as possible, like, I think it's Sherry? with the Bambi and the one solar panel. In any case, it's great to have a place to go with all these questions, and thanks again for the thoughtful answers to these and other questions. --Sarah