Sorry if what I typed was confusing, as I agree you can get the wiring in that zone without screwing up the rear 1/4 panel cards. But, if you start fixing mounting brackets to it, you will.
You will also still have the problem of supporting the weight of the amplifier on the original fixings, which will potentially trash the fixings.
As for cooling fans, what arethey going to do (not being funny, but I don't get it)?. If the space is all but sealed, a fan will do nothing but move the hot air around the chamber.
In order for the fan to have an effect it needs to draw in cool air and expell hot air - it can only do this if their is an inlet/outlet, which would require further modifications to the 1/4 panel.
I don't doubt it can be done, but I think the most important thing here is keeping the interior of the car as original as possible, and mouting the amp here is not the easiest way of doing that.