The problem I see with it is that it's not going to be receiving pushed air through it, like when it would be mounted in the front of the car.

It looks trick, but with all the rear-mounted cooling items I've ever seen, they usually utilize some sort of scoop or duct work that still takes in "pushed" or "forced" air from the vehicle's path of travel. IE: Toyota MR2's with the supercharged motor - the mid/rear platform, where the air scoops come out of the engine compartment up the rear pillar area and end there like just above the roof...