hey guys i have my 86 chevy s10 im working on been doing lots of body work lately with grinding down sanding bondo sanding again and using primer soon to paint. although i have a decent sized rust hole on the rear fender, i have already cut it out better and grinded the rust away.. i cant get behind it so ive been confused on how to fill it. i thought up of doing this, pretty ghetto but apparently works. you use expanding spray foam, spray it in so it expands out of the hole. then cut the excess away with exacto knife, then bondo over top of it to smooth it out and then primer it. any other ideas that dont invilve welding and can be done without getting behind the hole? ive heard of fiberglass but i think i would need to get behind it. or even cutting out screen from a window screen, adhereing it, then bondo? any suggestions are great. thanks!! need to safety this thing!!!