Check out what the guys from the "Trucks" show on Powerblock TV did for the custom front bumper they made for their ranger (rolling thunder) project. They used a 1/4" steel rod to make a frame with all of the shapes that they wanted, then stretched fleece fabric over the frame and solidified with fiberglass resin. They left it at that, but seemed quite flimsy, although you could add fiberglass mat to that smooth fleece shape to get your strength without going too thick.
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