I fit a four-inch 120vac van at the bottom of my fridge. It is plugged into the ac outlet near the back of the fridge used to power the electric heating element. The fan is pointed upwards to blow air through the coils. It fit in a small space and is held it in place with some bracing from the hardware store.
When my rig's plugged into shore power, the fan runs. If it's cold outsides, I unplug it.
When the rig is moving on the road, the wind velocity keeps the fridge well cooled.
Of course, the fan won't work if dry camping unless a generator is running.
Works for me.