I need help. =/

So i have a limited bit of space.. Funny because its a crew cab, but i run a business and need my racks.

Any rate. Im looking to build a 5.5 cube box. MAX parameter for width is 15.75. Height 39. Depth 16. all in inches..

I can give a little on depth but would like to see about keeping it at 16 so i can keep my console. 

Sub is a single mojo615d4.

Ive entered in data over and over but SBL has issues with what im entering and i dont know why. I really am trying, have been for days. =/

I get mad when i dont understand things and cant do them on my own. So here i am, swallowing my pride. Asking for help.