I'm really interested in how this build has progressed. I'm about to do something similar in my '06 XTerra and I really like what what you've done so far.
I'm especially interested in the enclosure you have for your sub and what you did so it wouldn't slide around in the rear as it's not carpeted back there (I had a mishap last year with a bottle of tire wet exploding and making my back trunk area a frickin slip-n-slide. It's much better now, but still has some excess slickness to it).
Please post an update. Inquiring minds wish to know!