I've had a few more thoughts about this since last posting. I think I see the way I will be proceeding, and am likely to order a Boss Bass 600 before the day is out.
I went and visited John H today (very nice fellow by the way), and not only got to check out his car a bit to get a better idea what audio options I want, but also got to have a look at what a stock subwoofer is like, as well as it's connector.
I am going to see if I cant source the female receptacle that is on the factory sub. If I can find it, I should be able to whip up a mini harness to allow for VERY easy installation of the boss bass behind the seat. No need to do any splicing under the seat, just plug and play operation.
For securing it behind the driver's seat, I plan to pick up a 3/8" square of plywood or whatever, partially carpet it, and have the back side a solid sheet of velcro. Then I can screw the boss bass directly to that board (does it have anywhere to do that directly, or will I need to fashion brackets?) and the board should offer plenty of surface area to not go anywhere when stuck behind the seat with velcro.
This will effectively make the entire unit completely plug and play. All it would even take to remove it would be unplugging one plug, and peeling the velcro mount board off of the carpeting. I'm thinking I might attach the little control pod underneath the driver's seat, facing forwards. I expect I will likely never need to operate it once I've got it dialed in, and if the LED is indeed that bright, it might even make for a bit of foot well illumination at night time.
If I do indeed find the receptacle for the factory sub, and make up a little wiring harness, everyone can be assured I will take pictures and document my work. I'm certain I'm not the only one interested in this sort of setup.