@Brent - it mounts on the driver's side wall of the trunk. It takes up surprisingly little trunk space. If you look under the left opening of your trunk you will see where a curved piece of sheet metal protrudes downward. This mounts underneath that curve and flush to it. Subthump's website show a picture of it installed. http://subthump.com/Chevrolet-GMC-Su...Enclosure.html
Another benefit of the "drop-in" box is that it can be easily removed if you ever do need the additional space. Just unclip and tape the leads and pull the box out. There is no cutting of the factory carpet involved (which helped when I had to sell the car).
@2010silvr - I was planning on keeping the sub to install in my new ride, but if you wanted it as a package I could do box and sub for $190 plus shipping (kicker comp vr dual 4 ohm)