You will also want to get some silicone to seal up all the seems. This will help make the box air tight. Some 3m spray adhesive and some speaker box carpet to make it look professional. Check out this link it well help you figure out the demisions you need to acheive the required cubic footage. I would go with about .75 cubic feet. The closer to 1.0 the more lower end bass notes will be dominant and the closer to .5 the higher bass notes will be dominant. .75 will put you right in the middle according to the recommendation. Though depending on the music you listen to, the more you might lean one way or another. ex. rap tends to have lower bass notes as opposed to rock with the highr bass notes. Hope this helps.
http://www.carstereo.com/help/Articles.cfm?id=5
this link has two calculaters one were enter your desired cubic feet and it gives you the dimensions, and one towards the bottom of the page were you enter your dimensions and it calculates cubic feet.
