i would use thin strand fiberglass, eithr that or make a milkshake of fiberglass resin and bondo (70/30) when it is about 80% dry use some 80 grit and knock it down to smooth... bud def use glass...
what i did on this cafe seat
80% dry start sanding)






then glide coat and some dyna gold


painted



not bad from something that started from this