Weight-wise the poly really doesn't make that big a difference after six coats of poly all around on a homemade airboat it maybe added a ounce or two at most. I used a rustoleum clear enamel spray and that melted the foam but i have been having a hard time finding any other kind of rustolelum that's not an enamel. Was it just the foam i was using or are there other non enamel sprays and I just have to look harder?