I wanted to share some measurements that may be helpful to people.
I removed my drivers seat, cut the carpet, and pulled out a large styrafoam piece out from the well.
I installed an amp in its place. The measurements that i can pass on are as follows:
L=16.4" (side to side. Note that the HIFI wiring harness runs along the side of the car and takes a bit of space. the dimension that i provided is the spec from my amp that tightly fit.)
W=10" (this is the front to back measurement. I had to cut the chassis of my amp to fit it in here but the inputs and controls are inset from this dimension by about 1.5 to 2".)
H=2.1" (I would not have wanted it any taller)

Those with the HiFi option have a pleasent surprise. The wiring loom runs along the side of the car and sice you have to remove the interior trim piece, the wiring is quite easy to tap into right next to where the amp is.

I installed my line level converter and crossovers on the floor under the seat as i drive with the seat all the way back. I was planning on building a small shelf for someones feet if someone was back there but i do not think there is room. perhaps i will build one to keep handy for when my wife is driving and the seat is moved up.

The amp i installed is a rockford fosgate P450.4 (i had to cut the front and back)

Thanks to everyone providing info on this forum! (and answering all my questions)

I do not have pics as my wife has the digital camera and is travelling.