What would you use for the "folded material"? That's what I had intended to use the Tyvek for, except that glue might not stick to it...
Well, that's happened, too. Not with this design, but with another rocket. I think the first improvement will be by using good quality plywood for the fins instead of balsa.
When I first started building this planform (Fat Boy cluster), I hadn't considered the longevity of the rocket. It was sort of a one-off to see if it would work. It does. And it's kind of fun to see people's reaction. I'd kinda like to make it more resiliant, and keep flying it.