Rick from raammat made a couple of these (don't know if he stil does), it's a 10'' Arc Audio subwoofer in a box that fits under 04+ WRX/STi front seats (the passenger side).
The specs on the sub are here: ARC 10D2
Awesome sub and I love the sound, but I'm selling most of the aftermarket stuff from my Subie, and this was the easiest thing to take out
The lip is pulled up on one of the screws, but it's been rubber cemented down and has no effect on it. If you want bigger pics, PM/ have questions, PM me.
Looking for $400, willing to negotiate.