ORIGINAL: acdii
Im making a mold to mold a cowl for my Dewey. The one it came with is too short for the 4 stroke, and it was cut up for the original motor. So I made a base plug from styro foam, and covering it with Bondo. When I get it to the shape I need, then will give it a coating of resin, polish it and make the final mold. I wish I could do what you are doing, it would have been done by now!
The bondo will dissolve the foam. You need to fiberglass the foam plug with epoxy resin. If it's just a one off, you can simply dissolve the foam away with laquer thinner after you have glassed it. What you have left is a fiberglass cowl.