Taken from earlier in the thread. In this photo, if I were to attempt this, it would be a two-part process to reproduce the extension. The existing piece would be used as a male mold because of the smooth outer surface, sharp lines, and no image of the condition of the inside of the fender extension. The second part of the process would be using the the first piece obtained from the male mold as a female mold. At this point we would have the smooth sharp lines of the male mold transferred to a female mold that would provide the smooth outer surface of the original piece. All of this would be much easier if the interior of the original piece was finished in such a way to allow it to be used as a female mold. Alot of sanding and finishing either way. And the resins used, mold releases, etc. have to be chemically friendly to the pieces being fabricated or it may melt in your hands.