I've recently completed another mod:
We experienced temperatures in the 90's on our last camping trip, and the fridge didn't work well. I decided to install a small fan to help ventilate the excess heat from the back of the fridge.
This is the back of our Dometic Fridge with the mod installed. The various parts are labeled. A thermal switch has been mounted to the accumulator tank with a zip-tie. It turns on at 100F. and off at 85F. Another switch (not shown) has been mounted on the side wall where it is accessible from the inside. It unconditionally shuts off the fan, or if set to ON enables the thermal switch to control the fan. The circuit is protected by a 1 amp in-line fuse/fuse holder in series with the 12 Vdc supply. The fan is a centrifugal fan that draws air in horizontally through the fridge vent and redirects it vertically to cool the condenser located at the top of the fridge. It is simply lashed to the pipe that returns the ammonia to the accumulator tank. The fan only consumes .15 Amp so it has a negligible drain on the battery, and it is very quiet. The total cost was about $25.
This photo shows the schematic diagram for the mod.