I have a custom box I just built for my 1997 dak cc for sale. It will fit bigger subs then the mtx thunderform. The bottom is fiberglass and the top is made out of 3/4 mdf. The air space is roughly 1.7 cubic feet. The mounting depth is over six inches. In my other box I have a 2 rockford fosgate he subs. They max at about 400 watts but I have one customer that has 1000watt subs in his. I also have fully carpeted the box and it fits nicely under the rear seats while they are in the down position. email me at [email protected] to see some pics or to get more info.