Well, dont forget to count your overhang, and the thickness of wood, thats going to take off a lot of your "space". I made my box 27x17 , and the top panel 33x19. The usuable space to put componants is only about 25x15 inches, due to thinkness of wood, and 1/2 inch clearence around area. So, you might need to take all that into consideration before actually drilling and all.