[Anyone have a box design for two x-15 d4's?]

So I purchased two of the sundown x-15 d4's and I'm looking for a box design with the subs facing up. I have a 2000 Escalade so real estate isn't a problem. I know one sub is calling for 4.25 cf so should i double that for two of them? If someone has a link to a setup with all the measurements already made up that would be awesome, but I just want these subs to pound so any help is appreciated.

[Box specs for two x-15 d4's in my Escalade.]

So just ordered two of the x-15 D4's that ill be running 1ohm with 3200 watts. I was just wondering if someone had spec's to that perfect box I should build for them?

I will probably have the subs facing up unless facing them a different way would be better?