Looks really nice. What's the false floor resting on? From what I can tell, it looks like it's just on the case and amps. You may want to attach some standoffs underneath for some more support. Additionally, you should really have the same airflow in and out, so swapping the 80mm fans for more 120mm fans might not be a bad idea. It'll also quiet it down a bit.
It looks really clean. This reminds me of my box a little, with the mix of fiberglass and wood. He is definately right about using wood wherever you can, it is much cheaper and easier to work with (at least on the flat parts).
Unless the speakers/woofers are wired out of phase there will be no cancellation in the lower bass/midbass, as the frequency increases you might run into issues but it really depends on the car.
Years ago (like 20 years) we had a subwoofer setup for the rear deck that had 2 x 8" subs facing each other firing through the rear deck of the car. The woofers were less than 3"apart with zero cancellation. the Ford "Shaker" system in the Mustang has the woofers on either side of the trunk facing each other.