Enclosure Questions for an X-15 in Nissan Titan

[Titan Audio]

I'm looking to build a box for a Sundown X-15 in my Titan and had a few questions concerning placement of the port, port area and volume of the box. The truck is a crew cab and the box will go behind the driver's seat and a Sundown 2500 running the sub. I have 30" x 21" to play with on the length and width and height can be whatever I suppose.

Sundown's suggested box for an X-15 is 3.3 cubes net, tuned to 32 Hz with 45 inches of port. What do you guys suggest? Also, what configuration would you suggest for the port, i.e.. "Sub Up, Port Up", "Sub Up, Port Back", etc?

Please let me know what you all think.

Thanks