Maybe OBG can enlighten us with some of the more successful habits of highly-addicted people.

Drug runners have to have some great tricks, right....?

One thing we once did at an ambulance company: converted a Chevy Astro into a multi-casualty-incident responce vehicle. Among the additions was 4 backboards, stacked 2 high, on the floor. Someone had made a wood frame to enclose them, but still flat so that it was the "new" floor. Perhaps something like that? You buy a few 2" or 4" beams, and a piece of 1/2" plywood. Elevate the plywood off the floor, throw the carpets on top of it, and suddenly the "floor" is back to normal. But you've got a ton of space beneath it, where the vehicle's true floor is.

http://www.ronshirl.net/images/Patrol/False%20Floor.gif

Kind of shows what I'm talking about. Yours wouldn't be quite so official, but shows the idea. with the trunk hatch closed, you wouldn't be able to see it was raised.

The other option is something in plain sight, that's not worth the consequences:
http://www.botachtactical.com/unmikpoldufb.html