custom stealth box

a customer of mine wants me to build him a replica JL stealthbox for his 2000 Lincoln Navigator. Now for those who are familiar with these, in the '00 navigator, the center console between the two rear seats are used. i recommended him a Polkmomo mm2104 sub. Now I know with some fiberglass and MDF i can pull off this box. I want to make it so the sub is firing down, and i was thinking of doing a port to get more bass of it, because the customer likes hip hop & reggae. Any input from the experience folks if its a good idea to put the sub firing down, and do a port? Or just keep it sealed? I am a little shakey on how to put the port so it sounds good.

http://mobile.jlaudio.com/products_...php?fit_id=1497

ported boxes are bigger than sealed boxes when each is at its optimum volume.if you are limited on space i dont recommend porting it,because doing so would probably sound worse than a sealed box closer to its optimum volume.after you decide if you have enough space to build a ported box the general rules for ports are keep the inside end of the port at least 3 inches away from anything,sides of the box etc.as far as diameter the general rule is for 8-10" speakers us a 3" port, for 10-12 use a 4", for 12-15 use a 5" and for 15 and up us a 6".then use the port length calculator posted above to calculate the lenth.