Sounds like a great plan. I've got the technology for woodworking and some experience with fiberglass, not so much equipped to weld.
I've been thinking about the crash thing, and I've decided that the best I can really hope for in a practical sense is to avoid causing the occupant more injury than they'd have if they were on the back of the bike. Thinking back to Senna's crash I'll pay special attention to keeping the struts, etc. from going through the tub. That could be messy.