Hi i am trying to get a Box made for my 15 inch Subs, it is going to be ported in the middle, My trunk is only about 40 Inches in length, 35 inches in width and trying to stay around 20 - 25 inches height .The thing is i need to know how deep should the port go down the middle and how wide it should be as well ??? Also what is a good wood to build it ????