I coated it on the outside with polyester resin. This sealed it and helped it keep its shape for the next steps.
I slushed the inside with Smoothcast 321 urethane resin to give it some thickness to work with, then I took a sander with 80 grit paper and knocked down the high spots.
With just a little bit of body filler and spot putty, it took shape fairly easily. I wet sanded it to 1,000 grit before painting it with white enamel.
All that is left is the leather straps to hold it on and a golf bag full of blunt objects ! Easy build !