Another little tip, if you decide to start from scratch.

This is a little harder than using urethane foam board.

I have built forms out of "hardware cloth"...which is just a large, very heavy, bendable screen. This method isn't really as good for rounded shapes. You can take some needlenose pliers and wire to attach pieces together. Make the form, and set it up so it's very stable, then lay saturated fiberglass cloth over it, and roll or brush until it conforms to the shape. If you have catalyzed the 'glass the right amount, you will have 30 minutes or more to work it.

Build up 4-6 layers, then skim coat with filler. It will really bond to the glass, if you put it on right after the glass "kicks".