You could always build a box like mine. You do have to give up the spare though, but hey I got free roadside assistance. http://www.prism.gatech.edu/~gte456v/images/top.jpg
http://www.prism.gatech.edu/~gte456v/images/bottom.jpg

No I dont smoke I was at my friend's who does and it was the best thing to give perspective. Second in the bottom picture the little thing on the bottom of the box is the thing my spare tire holder screwed into. When I got in my accident I hit the curb sideways so hard it ripped the rivets out of the metal. The box mounts flush in the trunk and I cut a hole in the carpet for the sub and placed a grill over it. The whole thing sits up a few extra inchs than it did with just the little spare cover but no big deal really considering you have a no cluttered trunk.