I did mine a bit differently. I kept the fridge mounted as far forwards as possible so as to avoid bouncy/rough roads making "camper fridge surprise" messes. Note: To maximize interior room in the camper, the fridge is only vented on one side (front of the camper in this picture). The bottom is open to the 3000W inverter compartment below it.
In looking at these fridges (ours is a TruckFridge 130L, similar to others of this size) the compressor and fan are on the top right rear when looking from the front. The fan is only 4", and the air flow is pulled from the outside, and blown over the compressor and coils, and exits on the sides and bottom. I figured as long as I created an air tunnel, it would cool just fine. So far so good....
I kept the vent small so as to avoid water intrusion issues. The black vent in this pic is all I have on the outside. I have 1" rigid insulation on the back of the fridge, and made a channel in the foam that allows the fridge fan to pull air directly from this vent.
Pick of the vent and foam from the inside of the camper
I installed a super quiet fan designed for home theatre systems on the coils themselves (attached with zip ties) and powered off the same circuit that powers the stock fridge fan.
This is the stock fan, wedged between the coils. Notice the arrows indicating the direction of air flow
This is the fan I added.
This is where I tapped into the power feeding the existing fan
Wired up and ready to go
They both come on at the same time. The extra fan blows the air out of the front side vent through another channel cut into foam on that side. The extra fan also has a "high power" mode. This fan is so quiet because it is actually a 12V 75CFM (that's a LOT of air) fan that is "dumbed down" to use 5V via a USB connector, so it runs slowly and quietly on your home theatre amp. I used a 45*C thermistor thermally glued to the top of the compressor and wired to 12V to kick it into high speed mode when the compressor gets too hot.
This is where the fridge lives now
With more and bigger vents, this complicated a system may not have been necessary, but it is working well for us.