Styrofoam would probably be too flexible -- you'd need to find some 'structural' foam. Like Royalex, for example. I have a Mad River Canoe that's made of Royalex, which consists of an ABS foam core (about 3mm thick or so) with a coating of vinyl on either side. The vinyl does a nice job of sliding over rocks and protects the ABS core from UV light.

On thing to consider: how would epoxy react with foam? I've had plastic and foam cups dissolve on me when I tried to hold paint, etc., in them...

Dean