have plan for 1sub but how do i adjust it for 2

[itzme218]

http://www.rockfordfosgate.com/rnt/rnw/docs/AnswerID_469-A.jpg
That is for 1 sub. Now i'm going to be getting another T2, so I know i could double everyrthing, (H x2, L x2, W x2, port x2) but that box would be huge. And besides it won't fit in the car, 27"x27"x52" is not reasonable.
How would I be able to get the same cubic inches out of it and tune it to 35hz?
Thanks. If no one is able to help i'll probably just take one of the sticky plans or just make two boxes, but I do want to learn...

[espguitarist91]

You can make your own plan using this calculator........http://www.subwoofertools.com/forum/ported-box.asp
Just put in some values and it does the rest. It takes port and driver displacement into consideration also ;).