Do you also have some experience in fiberglass
repair and/or fabrication? These eggs are laid up in molds, usually two for the exterior shell: top and bottom or left and right. Building from scratch means creating the molds. But there are a fair number of "project" status trailers out there that would make a good first go. The older it is the more likely there will be plenty of wiring and other mechanical work to keep you happy.
And if you come up with a really good solution to adding AC to vintage eggs (many of which can't structurally support an RV-type roof unit) without spending a marine-grade fortune... Well, you'll be a hero here!