I've not used Elmers brand epoxy resin before. But what you describe sounds a bit too thick. I use another brand (West Systems) which is about the consistancy of thick syrup. I've also used 30 minute epoxy from the hobby shop for small fiberglass parts. I wouldn't use anything faster than 30 minute, and prefer a slower epoxy. It should soak the fiberglass when spread with a brush. I do thin it a bit, perhaps 15-20% denatured alcohol. Thick frosting sounds too stiff. You can try thinning. Worse case scenario is that you'll have to lay down a new piece of monocote and try again. I would lay up at least 3 layers, perhaps even 4 of glass for a retract door, and use a plastic card to squeegee off as much resin as you can. Also, the squeegee will help to make sure the layers are well bonded and you have no air pockets. If you see any whiteish spots, add more resin and squeegee again. I would agree that PolyCrylic would not be the proper product for making free standing fiberglass parts.

Scott