Bondo shouldnt be used as a "layer" its better for filling gaps or correcting shape problems. If you are looking to reinforce your pep, do a layer of sealer (polyurethane spray works great) then fiberglass resin, then do a filler like bondo, then 2 more coats of resin is what i use, i also do 1 coat of interior resin and a layer of fiberglass mat on the inside fore reinforcement, if it needs it.