I have been using MinWax polyurethane for several years now to fuel proof my firewalls and tank compartments. I never use epoxy anymore for fuel proofing. Two coats and the surface is good to go. I have not been happy with the spray cans and now apply from the can with a foam brush. The final coat must be lightly sanded. I've also applied silkspan and light fiberglass over sheeted balsa with good results. I used it to fuel proof open bays of Koveral and was disappointed. But I think the fault was mine. I didn't mix a filler such as talc, corn starch, or micro baloons. I think with a little filler, the results would have been very good.