The distance from the front to rear is supposed to drop the temp by 200-300 deg.
You're only fooling yourself to think you will get that much of a temp drop for air traveling thru 12 feet of tubing, relying on the disapation of heat from surface heat transfer. The pipe will heat up and the air moving across it at high speed will disappate some heat but probably more in the order of 80 deg F.
....which should be enough to prevent serious detonation but will limit the true capabilies of an intercooler that will drop temps by 200 deg F.
I don't like the idea of sucking engine intake air from the rear of the car.....the dirtiest air available.