Chevy Astro Stealth sub install idea

LOOKING FOR INPUT ON AN IDEA I HAVE...

I have a 1993 Chevy Astro extended van.  I want to install a subwoofer in the van, but need to do so without putting an enclosure under the seats, in the cargo area, etc.  Two reasons: 1. the van is used to haul the kids around 2. I want the system to be as hidden as possible.

There are plastic factory cargo boxes around the rear tire wells on both sides of the van.  In front of the tire wells they have deep compartments, drink holders, etc.  The passenger side houses the spare tire and jack behind the rear well, but the drivers side rear box has only shallow storage boxes and better than a foot of dead space beneath it.  It looks like the cargo boxes simply screw to the sides of the van over the top of the interior panels.  How much space is behind the panels I don't know. 

I have this idea that I could build an MDF enclosure mounted behind the cargo box on the drivers side rear and put a grill in the face of the plastic cargo box.  Burgandy grill cloth and only somebody really observant would even know it was there.  I figure a 10" woofer (maybe a 12") is the most that would fit there in a sealed box to limit the box volume.  I have about 1 cubic foot of space to work with so I am thinking either a Solobaric or a DSQ woofer (from Dayton Speaker via Parts Express).  Not looking for huge SPL or anything, just want to improve the bottom end as much as possible without intruding on the van interior too much.

What do you think?