According to system 3 literature, epoxy will bond to sanded polyester resin, but polyester will not usually harden if applied over epoxy. System 3 makes one specialty epoxy, over which polyester will set (SB-112: expensive, but it also has some UV protection built in.) This info is from the epoxy book, downloadable from www.systemthree.com .

Replacing all the fiberglass IS a lot of work, but can be done: http://www.myccr.com/SectionForums/viewtopic.php?topic=522&forum=20:

: I've been asked to take a look at a wood/fiberglass canoe built in the mid
: seventies. I assume that it was made with polyester resin. Is it possible
: to repair and/or recoat this with modern epoxy? Any particular concerns
: about preping the old surface to bond with epoxy? I have not seen the boat
: yet, but it is being described to me as having a "deteriorated"
: fiberglass coat and I'm imagining that it will need to be taken back down
: to the bare wood. Probably more than I want to get into.