Being in Portugal, there's no Smooth-on or URAC 185 around here that I can find. What I use is an epoxy resin made for boat-building, also used for making skateboard and skis, that works very well in wood/fiberglass laminates. It cures at room temp in about 6 hours, is sandable after 2 or 3 hours, and cures fully in 24 hours. It also has an adequate amount of flexibility once cured, which is why it is successful in skateboards and skis. It is called Epofix 2000. I will try to dig out the spec sheet that I have somewhere.
DF