I keep things that work well for very long periods of time, so it has been important not to choose rv units with compositions known to degrade terribly when typical aging issues take their toll over time.
My preference from that perspective has been to avoid the wood frame / wavy skinned units and membrane covered wood roofs.
Our rv's have been aluminum wall and roof frame, aluminum roof skin, and the current Intech trailers are also aluminum base frame and aluminum exterior skin, to boot. Aluminum framing is more tolerant than wood of rainwater leaks that may occur!
Friends of mine with diesel pushers enjoy well-turned out fiberglass end caps, composite sidewall exterior skins and aluminum or compositr exterior basement doors, so generally are properly constituted for longevity.
If you are indeed handy enough to build out your own rv from scratch, I would suggest that you perhaps look for a dowdy or dated interior diesel pusher with a solid driveline and sound exterior, then gut the interior, building that portion to suit yourself.
Lots of aging DP MH's out there that are not pretty enough for a prospective buyer's wife to enthusiastically embrace, but for a self-build project will have important reusable basics already in place such as fresh/grey/black tankage, generator and basements with wet bay.
Consider aldo the time required to build up your own. Some people start with a bare passenger bus, then have to deal with getting it "all the way there". Often see those for sale unfinished, too much effort for the initiator to complete...
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