i have been using cheap bondo polyester resin to make fg cowls and vents etc for my airplane. however, i have had to use about 8 layers of 1.5 oz on these parts to get enough stiffness. I hear of glider fuselages made with 2 layers of 2 oz cloth, how are these stiff enough? is epoxy resin stiffer than polyester? can any epoxy be used (as long as it is thinned)? is epoxy heavier than polyester strength wise/layer wise? thanks a lot