I made them from MDF but 1/2" plywood would work just as well. Took some trial and error to get the fit right. Good thing is that, once you have one side fitting, you can just reverse it to make the other side. Then I just used some 3M spray mount and some cheap carpet from Home Depot to cover them. Are you doing the speakers up front too? Those give it a cab-filling sound but the amp makes all the difference.