4 jl audio 12w3v2's

These drivers are 4% saggy if used as down or up-firing, close to maxing out at the limit.  5% is maximum  sag factor.  I would use these as front firing or firing at up to a 45 degree angle.  You can follow the box dimension outlines set forth in the JL manual, or you can use that as a guide and work it up a little more precisely using WinISD Pro.  See sticky subject above if you want to get more involved in a hands-on approach.

Sealed is best SQ for this subwoofer.  A 5.5 cu ft (net internal volume) box for these four subs will sound good and work well.  But if you are more inclined to maximize SPL, use the vented box approach.  Manual indicates 7 cu ft tuned to 30.8 Hz, which would equate to a 4" X 12" slotted port opening at 13.7" long.  You can, instead, flatten the response for a better sound quality by building at 10 cu ft, tune to 25 Hz with a slotted port 4" X 12" X 15".

All box volumes are net internal after allowances for driver displacements and bracing.  I would face the port to the same side as the drivers face, probably look first at firing slightly upwards toward the rear.  Work angles into your design with the help of this calculator and also the ones supplied by the12volt found to the left column of this page.

Do you have the dual 2 ohm version of this sub?  Putting a 2 ohm load onto each amplifer?