Fiberglass rear bumper brackets

So I picked up a fiberglass rear bumper for a steal at a swap meet recently and since then have decided to make my own rear bumper brackets from fiberglass, from scratch. I had never worked with fiberglass before so I initially failed miserably, but I have learned and think I may be able to do it now. If it works I may post a "how to", if not, well, I guess it better work. Has anyone tried making these things for a 70-72 dart before? tips? suggestions?