Is it possible to fit a 12" shallow mount sub under each front seat of the '99 Accord sedan? What I want to do is put this http://tinyurl.com/yc26vpm in the trunk and two 12"s under the seats. Whats a good amp to make this happen, and is it possible for the 2 under the seats?

 

there is no reason to try to fit two more 12's under your seats and expect them to keep up with the prefab 3-10" enclosure you have linked. regardless, i've removed the seats in my 2001 Accord and there isn't more than 4" under there with motorized seats. If you don't have motorized seats (LX or DX) then you may have another inch or so. Lastly, try to avoid mixing sub sizes and enclosure types unless they are playing different frequencies.

Regardless, you'll have phase interference from the front subs arriving much sooner than the trunk subs.

your goal up front should be midbass - which is best achieved with beafy door speakers. Take the money you planned on spending for underseat subs and put them into some awesome component speakers and sound deadening/pods for the front doors. maybe some shallow 8" subs under the front seats for midbass (not playing the same frequencies as the subs).