Note: This ventilation idea was a failure. It is just too hot in the summers to adequately ventilate with outside air.
My broken thermistor wire problem on my trip this summer dramatically revealed the conditions behind the Isotherm refrigerator in my van. It was very hot back there. I used a towel rolled up to block the heat streaming in from it after I opened it up to try to fix it. I had put insulation all around the refrigerator leaving a hole above the compressor and behind the entire refrigerator open to the upper and lower vents. I assumed the compressor fan would be sufficient to draw air in and out. Crossing the Great Plains meant very hot conditions in the 90's to over 100F as well as uncomfortable humidity levels. Added to that was my westward trek meant the refrigerator side of the van had the sun beating down all day as well.