[jime57]

I really don't have any experience with cardboard/fiberglass or foam/fiberglass material mixes. I think that one might want to do some material testing before getting too far along - assuming lack of experience like mine.

I know that fiberglas cloth/resin needs support to hold any shape while hardening. Therefore, it must be laid down over some sort of full support. I also know from personal experience that resin is not compatible with styrofoam. I have tried to mix it in syrofoam cups and it just disolves the cup. A while back I discussed this with someone in the ecomodding community who indicated that this problem could be sidestepped by painting the finished styrofoam shape with a water based latex paint before fiberglas overlayment. No direct experience, but I've heard it.

Regarding cardboard/fiberglass, there may be shape shifts (ala Star Trek ;-)) when the resin soaks into the top layer of cardboard. I think that I would certainly do some quick testing on this approach before I got very far along. In addition, it is going to be difficult to get finish quality smoothness with just cardboard and fiberglas. It will probably suffice for testing, but it's gonna be difficult to get it smooth. Perhaps the addition of some exterior bondo will facilitate the shaping of finish quality curves.

All this is just thinking out loud. I also want to build a boattail, but getting the materials tested before I start is definitely on my agenda. Too much work and expense to gamble of bad material mixes. Perhaps a two step process, with cardboard over frame, followed by something more permanent, would be the best way to go, but that is really slow. I'm still rolling it all over in my mind. Perhaps someone else will go first ;-)