Kodiakz's thread about his box is here. Some of the pics below are from that thread. This box seems to be the best way to maintain the intended usefulness of the Av's design and achieve more output than an underseat box can muster.
It's (JL box) supposed to be out right after CES. The cost between the Stealthbox with the W3 subs and having your own midgate box done will be quite substantial I would suspect.