alpine 1542

Noob here LOL. I am trying to build a custom sub box to fit in my Jeep. I want it to have a square port, The total box size is supposed to be 18" high X 16" deep X 28" long. My 15" Alpine Type R 1542 is going to be installed into it. I would like the box and sub to be tuned at 34HZ. I followed...