I stumbled across this
http://sparetirebox.com/gallery/gall...e%20Tire%20Box
which seems like a good solution, still cuts down on your trunk size, but it leaves whats left of your tunk safe for every day use throwing in bags, coolers, boots, etc.

course now i'm thinking of adding a 2nd 12" ... hmmf. (the bass hits help your understeer, if you time them right, er something)
here's my last 100 + lbs box.
btw if anyone wants this box , and amp mounting boards i'de probably give it away for free. the box had about 2.8 cubic feet of airspace until i glued in about 1.8 cubic feet of wood, (that's why its so heavy, you could probably knock/ tear out the blocks of wood) and it would lighten up a lot. and or just remove it for autoX / track use .