Dust build up can be a significant issue with efficiency.
I don't know how easy it is to access the fan on a chest style fridge, but this is about 6 to 8 months of build up in my Van
Obviously a detriment to heat extraction, and this is why I added an air filter to the air intake. The blades still get some build up though. Much less than without and it accumulates slower and affects airflow much less than in the photo.
Heat extraction is also very important for compressor and compressor controller life. The controller has a heatsink on its back side. Airflow across the cooling unit is your friend.
Also, the Danfoss compressor controller can handle powering 0.5 amps of fans, fans that fire up only when the compressor turns on.
The fan in the pic above consumes only 0.05 amps. The controller could power 10 of these fans. The fan which came with my VF c51is is 0.12 amps and rated at about 70CFM.
Tinkerers/ macguyverists could pretty easily add another fan to help extract heat. Two of the Noctua fans would likely draw less than the provided fan for less energy consumed to power them, and extract considerably more heat in a push pull orientation, decreasing compressor run times noticeably, especially in hot weather or when one drops a warm 12 pack into the fridge.
http://www.ra.danfoss.com/Technical...f_electronic_unit_ac-dc_04-2009_ei100g402.pdf