Tonight I got one of the woofers installed into the underseat enclosures.  
Parts used this step:
- 3/4" mounting ring provided in kit from MusicarNW
- 4x #10 x 1" screws to mount wood ring to enclosure
- 4x #6 x 3/4" screws to mount woofer to wood ring
- ~18" of 16x4 shielded wiring, using 2 strands each for + / -
- A couple pieces of shrink wrapping
- Some more of the weather strip foam I used before.
I put a strip of the foam under the wood ring between it and the enclosure and another piece between the speaker frame and the ring.  This was just enough to lift the speaker off the bottom of the enclosure.  Definitely have to be careful not to tighten the screws too much or they'll crack something.  
I ran the wire through the hole provided in the ring and soldered it to the speaker, then covered the ends with the heat shrink tubing. Some lessons learned:
- I used the second speaker ring to set the speaker on upside down.  I'll use the same ring for the second speaker and then put the wire through the ring after it's connected.
-  Taping the wires to the magnet held them in place so there was one less thing to hold.
Once it was all put together I set the grill on top.  It looked like the outside part (as it would sit in the car) may rub as the speaker's foam ring moved (I'm not sure how much extension these speakers have, there was a bit of room, but not much).  Simple enough to take the dremmel out and grind off some of the underside of the grill.
I got a small soldering iron from home depot, worth the $20 over my big old gun.  Also got an automatic wire stripper from radio shack - makes stripping the wires so much easier.