I am trying to design a wall for my van but the programs and math fourmulas i am using say three differrent things. one says 111.4 inches long and one says 1.2 inches long and and the last one says 4inches long the box is 19.86 cubs net before port and subs I want tuned to 54 htz and yes its only a burp box port should be 41 tall and no more than 15.5 wide sence thats how deep the box is inside and i would like to have atleast 250 square inches of port no less. Its for two hifonics goliath 3215"s wich are 15" subs. I will be using threaded rods for brasing the front and back of the box.