I've been running fiberglass front, rear and running boards on my 37 for 7 years without any problems. No spiderwebes, no cracks and I drive it regularly. I also don't mind standing on it for some speed now and then and still no problems. Fit was pretty good. I got mine from R&R in Tenn.
It makes a difference if the fiberglass is hand lapped or if it is sprayed. Based on "what I hear" the sprayed ones are more prone to cracking and also having thin spots.
Most folks "thump" my fenders and still don't believe they are fiberglass.
Just my nickels worth.
