Well, am I designing something for a 8" L7 or a 15"? Also, what are the max dimensions that will fit in your trunk. This information is needed before anything can be set in stone.
It would work, but I prefer a tad lower around 35Hz.
You could build this...
it'll be decently close to 3 cubes flat once the sub is dropped in and has plenty of port area and tuned to 35Hz. That box should slam rap music pretty well for a nice daily setup.
RE Audio is even nice enough to make a nice little cutsheet plan for you //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif
Well, it would increase the volume and lower the tuning a tad.
go to http://www.reaudio.com and mess around with the box calculator until you get the volume and tuning you want that will fit your trunk's dimensions.