Trying to get my '69 Barracuda ready for the track this spring. The doors back is original sheet metal the front end is fiberglass. I have ~1/2" gap in between the fenders and the doors so I need to build up the edge of the fenders. What should I use, something like a kitty hair filler or something specific to fiberglass?

Also, going cheap on this car but was wondering would you use Rage Gold filler ($58) or "Bondo" brand filler ($20) for the finishing work? I've always used Rage.