Paul,
It's nice to hear that you've done some of this (even though it wasn't epoxy resin) and that the boats have held up. That's really the only concern that I have, is longevity. I have very little experience with PE resin, other than helping my Dad repair small craft, but it seems to me that it always created a real thick/heavy layup (probably from in-experience). If canvas/nylon/poly is strong enough on its own (just needs to be sealed), than I don't think that it will require much epoxy or heavy glass cloth. Somewhere in there you cross the line of having a durable, but flexible finish to one that's so thick it becomes rigid or even brittle (and heavy). Nobody wants to build heavy kayaks, but from what I've seen so far, the durability with epoxy and 6oz glass is worth the extra weight. The model that I built and the sample panel will be put to the test (finally) and I'll share the results soon.

Good luck on your boat,
Keep us posted,
Scott