I have designed a kerfed ported box for 2 12” Rockford fosgate p3D12’s. I have the H=18 W=40 D=18 with a 4 inch kerfed port between each sub. When I multiply the HxWxD and divide it by 3456 for 2 cubic ft I come up with 3.75 cubic feet. Will this box be to big or should it work and sound good? It’s going in a 4Runner.