bukjep

I've gone through almost 20 pages of this forum and still not sure exactly how I should build a box. I've got a general idea, done some research, but I'm hearing/reading different things. I plan on purchasing a fully loaded 18" BTL very soon, but want to get the box out of the way first. My max dimensions I'm working with are, 39" Wide, 20" height, and 24" depth. I want it to be sub up, port back. This is going in the rear of a Nissan Pathfinder. I'm also wanting to get it tuned to around 32-33hz, that's where I'm having trouble. After sub displacement, and a port tuned to that frequency, how much cubic feet would the box be if it was built to those max specs? Just from a straight up box dimension, that would be over 10 cubic feet, correct? This doesn't factor in sub and port displacement yet. I've entered in a bunch of different vales into the reaudio box calculator to try to come up with a box, but after reading on the caraudio forum, a bunch of people say its not too accurate. Thats why I came straight here to try to get some help on making this box. If anyone can design a box using those specs, and maybe even provide cut specs, I would appreciate it very much. If anyone needs more info, feel free to contact me at [email protected]. Thanks in advance.