I've only done a very small amount of fiberglassing, but I've found that the best resources (sorta) are caraudio sites. Some of them have fabricator's forums and the like, and since fiberglass is a big part of custom stereos, they often have some very good ideas.
This thread taught me the most:
http://audioforum.termpro.com/cgi-bi...;f=32;t=000549