Dennis, I was going to do just what you stated but the vent on the roof has a screen (plastic) to keep stuff out. Did you cut through the screen to install the fans? I could make a bracket to hold two fans and a thermostat and then pass the wires down the back of the refrigerator to tie into 12v power. Should add a on off switch so they don't run when the unit is turned off.
On a earlier unit I replaced the cooling unit and found the replacement cooling unit required additional cooling at the condenser. I added fans and used an attic fan thermostat to turn them on and off. It was adjustable so I could set it for what temperature worked best. As I remember the condenser needed to be around 95 deg for the unit to cool.
For this trip I am going to add clips to the fan leads such that I can clip onto the 12 power feeding the refrigerator, that will get me through the next trip. Then I have to fix the problem.
Thanks