Hi:  I have built a mold for a fender, and then made many copies of the fender known as a tire Hugger in the sport bike market.  I have shipped as far away as Australia.
The mold was a very simple 5 layers of glass cloth and Flag resin. The support system was half inch pink foam insulation board bonded to the bottom of the mold.  The fenders are made from Low vis resin. two layers of cloth layed on a surface coat of flag and cab-o-sil.