I have to agree with Ron, epoxy and microballoons. Seal the hull first with epoxy(I personnally prefer West Systems but it's spendy), spray on a coat of primer and sand. Fill any low spots with th epoxy/balloon mix and let cure. Next, sand as needed and then repeat the primer application and sanding. Do this until the hull meets your approval and then paint as desired. Be sure to clear coat the paint so fuel doesn't ruin your finish