My sub is a 10 inch, I had a *custom* downfire box and i didn't like it. and the sub hits the seat only when I crank on it witch is almost never

 

They make a 2" back seat lift kit.....i dont know who or where makes it but you can search it on google.

 

i built a box for mine. i had an infiniti sub from my last truck, and i couldnt afford a new one, so i made the bottom of my box out of fiberglass, only about 1/4" thick, then glassed mdf sides onto the glass bottom, and put a top on it. the speaker does push into the seat enough to leave an imprint, but it sounds great. it actually sounds better with the seat down than with it up.