Ok..>I have one Fosgate P2 10" sub and right now it's just sitting in a box on the back seat.

Sounds great back there but it's just in the way. Soooo...I'm not sure what the dimensions under the seat are and the P2 is a 4ohm 400 Peak Watt Sub so it's got a HUGE magnet.

So in your opinions...if I can get the box cut down enough to get it under the front seat....how do you think it will sound?

Should sound fine. I belive I read somewhere that a 10 only requires like 1.52 cubic feet of air space.

ONLY 1.52ft3? That is a whole lot of airspace! Maybe if your going ported. Alot of subs run at 0.6ft3 sealed and theres some that can go as low as like 0.4ft3.

I was thinking that it was a little big..I have some 1.5 cu ft boxes for books and they are pretty big.

One of these days I will be getting around to building a box for each of my 8 inch Kicker L5's. These subs only require 0.33 cft. and sound great. I plan on putting one under each front seat. The only issue is that I have been "trying" to get around to this for almost 2 months. Oh well, they do look pretty cool sitting in my office with my Kicker amps .