I made some fake fenders out of XPS 2" foam. Covering them in PMF might not look very good. To many compound curves. Would coating the XPS foam with fiberglass resin work to make them more ridged ?
I have not heard of epoxy used in auto body. Look up West System epoxy it's used for boat building , and airplanes. I used it for my tear. This is the cheapest place I found it. http://www.discountmarinesupplies.com
Best way would be to make the fender the "plug" for a mold, then pull a mold from the plug & lay-up the fender out of glass as the finished part from the mold. Sounds like a lot of work, but it would be a good lightweight fender that's strong & repeatable. I know, too much labor & cost of materials...
Build log: viewtopic.php?f=50&t=60248 The time you spend planning is more important than the time you spend building.........