try sub up and 6" port to the passenger side...it worked for Clay A team's MX3.
use of a termlab will make tuning most effective.

My current box is 13" high, 19" deep and 20" from side to side. I have one port 6" in diameter by 6" long. (It WAS 2 ports, each 8" long but were slowly cut down to the one) Sub is facing up, port is facing back. I have tired facing the port to the side and it's not as effective as facing the port to the rear, on the driver's side. I'm doing a 141.1 on the term lab.