Auto body repair & detailing: Using fiberglass to repair a quarter panel, synthetic motor oil, rust removal

Question
I have a '73 Nova, and both the wheel openings in the rear quarters are suffering from body cancer around their upper edges. The rest of the sheet metal is in really good shape, so rather than replace the quarters, I'd rather just patch them up with fiberglass. Problem is, I've never really used the stuff myself. I'm assuming all the normal surface prep needs to be done (rust removal). I'm thinking of using that P.O.L. (Paint Over Rust) stuff to get into the really hard to reach places. I don't know, though, if it will be compatible with fiberglass. Any tips you may provide will be a help!
Thanx!

Answer
If you are going to patch the cheap and easy way, do ahead with your POL stuff, it can't hurt. Once you get all that done, go behind the panel with rust proofing just in case. On older cars, I use a mix of used synthetic motor oil and rust proofing. The oil will soak into the rust slowing it down from coming back.