I supplied the amp and speaker to my installer. I get all my parts from Sonicelectronix.com (amp + speaker was $530). The installer charged me $600 to build the box and install everything (install parts included), which would put the cost of the box alone in the $350 range.
The amp is a Kicker zx400.1 The speaker is a 12" JL audio 12w6 dual voice coil. Wired in parallel, it is 1.6 ohms, both rated and on my ohm meter. The zx400.1 is rated at 400W into 2ohms. At 1.6 ohms, it is 500W rms (tested).
The box is coated in a black vinyl with color and texture just like the plastic panels in the rear hatch. The base of the box is done in fiberglass. They layed down sheets of tin foil on the carpet in the rear hatch, then layed sheets of fiberglass over that, then the hardening agent, to build the base of the box so it fits the cargo hatch perfectly (the tin foil was just to protect the carpet and once the resin dried, the foil was removed). The sides and top are MDF particle board. The bass boost control is in the center console next to the the Ipod connector.
The box fits very tight, but can easily be removed and does not rattle in any way. The box is 2" taller than the aluminum cross brace, but does not obstruct rear view in the mirror, or looking over your shoulder into the cargo bay. The flush mount area for the amp is actually a boxed in recess with a sheet of vinyl over particle board with a cutout the size of the amp, then the amp bolted to the back side of the particle board. If I wanted to change out to a bigger amp, They would just have to re-cut a bigger hole for the amp to mount a new one.
I have the sport/touring model with nav, so this is in addition to the stock bose nav system. It sounds fastastic. My first speaker was defective and my installer gave me a kicker CVR as a loaner and the sound sucked in comparison. The Kicker was probably 2 db louder.....which is noticable. But, it rolled off around 60hz, so the sound provided was 30-80 hz and that's it. I had a big gap in the frequency range between 80-150 hz until the stock Bose system started to come in. When I got the JL audio speaker, it was night and day. It still gets louder than I need and can easily overpower the stock Bose system even though it is not as lound as the Kicker speaker was. The JL speaker doesnt start to roll off until around 120hz and with the amp set at frequency center of 100 hz, it fills very nicely all the way up to 150hz and meets up where the Bose system starts to fall off.