First what subs are you looking to run? if it doesnt matter then I can probably take some measurements for the rear. You will have to decide if you want to have two seperate boxes or one big one. I removed my center seat in my 99 and built a prototype 3 10" box that is a one off custom. After that I have built a few 2 10" for the same place. But the mega cab has room behind the rear seats that noone else has. I have done a Nissan Frontier ext cab with 3 8" behind the seats that hammered!! Of course my 3 10's slammmmmmmmmmmm. On tuesday my entire system must be removed out of my 99 to be placed in the 06 that I havent decided what I'm doing in yet. I will probably fiberglass the entire underseat storage area for my 3 10's and post photos. Email me and we can talk. I can get any mobile equiptment you want or desire and will ship finished boxes to you. Thanks for your time, JD.