If you have a compressor refrigerator
like the Waeco for instance, it is essential to cool the condenser. This is where the heat from within the fridge is extracted to. As the ambient temperature rises so the efficiency of the fridge falls.
What I usually do is to put a simple computer fan, which takes virtually no current
, and point it at the condenser. Then I make up a cowling to ensure that most of the air from the fan goes onto the condenser and is drawn from below the fridge ie the cool bilge
Then I make sure that the air rising from the condenser, which will be warm, flows out into the cabin
rather than remain behind the fridge.
The fan is wired up to the fridge so that when the fridge is on, so is the fan.
The ducting can be of any stiff material, taped into the shape that you need.
This has always turned my fridge into one that does not make ice cubes into one that does!