Location??
If you make your own and use plywood, you can topcoat it with a polyurethane top coat. I made a replacement transom for my brother's RIB using 1" plywood, then sealed with urethane primer and finished with a urethane top coat. It came out decent and looks like it's made of something other than wood. The one inch think marine plywood is available at Boulter Plywood in Medford, MA. I believe they will cut to size for you for a fee.
Also, if you like, I can measure the casting platform for my 306 Canyon. If it's the same size, then you could order one from GW, if they don't still make the one for your boat.