RE: fiberglass covering question-blisters in sun
I have used the Poly C method for years, and haven't experienced this problem.
It may have to do with the method of application. If Poly C is applied heavily, it takes much longer to "cure" than if applied in light coats. I usually wait at least a week after application, before I sand and prime. This allows plenty of time for the water to evaporate.
I usually apply 2-3 light coats of Poly C. The weave is then filled, (after 1 week) with high build automotive primer.
I feel that patience is the key. The poly C method is easier than using epoxy, but not necessarily faster.