On the other hand, I may try an alternative solution, using a number of peltier elements. I have five peltier elements, each 4 square inches big. I am thinking of creating a duct where they are mounted, dividing the duct in two, with some serious heat sinks on each side. Then blow air from the cold side into the car and venting the hot side to the outside. Right now it is just a thought, no serious planning has taken place, but I have studied the possibilities and challenges involving peltier elements.
Some years ago i made a mini fridge by using a peltier element. A total failure!
The peltier element get realy hot on one side, and very cold at the other side. The peltier element is just a few millimeter thick. So there is just a small space between the hot and cold area. The problem i had is to make proper heat isolation. Keeping the heat away from the cold. A big part of the heat was heating up the surrounding of the peltier. The heatsink on the inside of the fridge was realy cold, but the heatsink on the outside was heating up the housing of the fridge.
Result: the temperature of the fridge has raise a little after 30 minutes of heavy power consumption.