I use a TC-3000/Audiopulse Axis in a 3cf, sealed box powered by a Behringer EP-2500. With a Behringer Feedback Destroyer as an EQ to lower the inductance hump at 55hz and boost the low end. If that is outside of your budget, then there are dozens of other subs. What is your budget because we can go from the Dayton Quatro to the Audiopulse LMS?
The Soundsplinter RL-p 15 dual 2 ohm. It has a low Qts of .333. I would want to the Vas to be closer to 140L like the dual 4 ohm version but 163L is still in the acceptable range. It will handle gobs of power so you can easily push it with a pro amp.