is there any way to install subs under the seats, or is that over-doing it? i have a coupe, so the front seats slide back and forth for access to the back seats

 

Nothing is impossible, but you are going to have a hard time finding a "sub" slim enough to install into a box and then fit under the seats, even a JL audio 6w0, [6.5"] has a mounting depth of 3.5", what you need is something like the old Alpine SWS-BE45 "bass engine" go to http://www.alpine.com click on tech support, then consumer site, then product technical info, then product feature & specification sheets, then subwoofers, then all the way to the bottom and click on SWS-BE45, to get an idea of what I mean, you can still get the original at http://www.aurasound.com