have you ever worked with fiberglass before? i have know people that made their own fenders and they turned out good.... companies make fiberglass fenders... really depends on your experience and if you know what you are doing.... fiberglass can be pretty messy though... you will need to setup molds, etc, and get the glass layers and deal with epoxy, etc.....
and i know i am a total ass, but dont you need to figure out what you are going to do with 2 worthless trucks before you start planning and building a fiberglass body parts?