You said "beefy 10"? Do you have a particular one in mind? The way I put a baffle board on the back wall and use fiberglass for the rearward part of the box takes up NO CLICKS on the seats. The only draw back is that you have to lose the jack or anything else mounted behind the seats. I can fit 3 JL Audio 10W1's or 10W0's and the amp under the passenger seat, or 2 shallow mount 10's (less than 6" deep) of what ever brand and the amp ressed into the center of them. It is very easy to do and cheap. Requires minmal fiberglass knowledge and a lot of patients. i get almost 3 full qubic feet of air volume in this design. It's not rocket science!
-Measure from the back of the seat when at full back position from the floor up to under the plastic below the window
-cut a board of at least 1/2" thick MDF to fit the space
-Figure out where to mount the subs so they don't hit the back wall or the hump at the bottom of the floor
-When you have them postioned correctly, use cardboard as template to contruct divider walls for the subs, or french in a square for the amp
-To seal theis air space pull everything (carpet, plasric strip beloww window, etc...) and line it all with alluminum foil
-Then line it all again with clear plastic wrap
-Now lay in some thick fiberglass matting and goup on the resin
-while it's setting up, screw the MDF together and put it in place
-lay in some matting for the side peices and goup it up some more
-When it all sets up good you can pull the whole thing and remove the protective wrap and foil, push the carpet back down, etc...
-I'd sand and paint the new box, wire it for the subs and amp if you mounted the amp on it, and stuff it full of poly fiber to tighten up the bass
-If you opt to wrap th face of the box/amp rack with material, put it under the plastic window trim before you tighten it back down (very pro looking)