Jim, I'm amazed that you bring this up now because lately I've been thinking a lot about this very sort of thing. Of course, you amaze me a lot

But, what you're talking about is probably true for all of us. I want/need more flexibility in my shelter/sleep system.

Right now I'm working on designing a sort of modular system that allows me to "Mix and Match" according to conditions. So far I'm using 3M's blue masking tape (it is easily removed) and visqueen to mock it up. I have a long way to go before I'm ready to start sewing silnylon and bug screen.

I think the concept has promise, though I'm not too sure there is much of a market for it. Modular designs potentially do many things good, but none of them exceptionally great. Still, it's really no surprise that you see the concept in use already by your homeless friends. They are motivated by need, and necessity is indeed the mother of invention.