74 Duster 4 banger Street/Strip Build

I'm gonna need to do some rocker panel repair this weekend. That gets me thinking on the quarter panels. I was thinking AMD half quarters.....but I also see VFN fiberglass offers fiberglass half quarters. Fiberglass = $380 a pair, AMD = $600 a pair. Fiberglass = light. My main question is....does fiberglass = dependable and no cracking where it meets the old metal? I mean.....I'm not building a show car, but I don't want a Crack in my paint

Just flange the quarter and finish out everything nicely then Dzus the fiberglass into position. It will make it easier to service and adjust the rear suspension and tires in the pits. I know you strive to make things light.