[bobcowan]

Make it out of aluminum; light weight, inexpensive, and easy work with. The dash has some curves to it. Trying to get those curves in plywood can be done, but it's not easy.

Bends and curves will not add any strength, but will add rigidity. If you put a bend in the bottom of the dash, and then secure it to the firewall with another small panel, it will be plenty stiff enough.