@ Aage, I tried that method amongst my alternatives. It is less efficient and I had better performance for less dollars. The crafted solution totaled $40 and the 'old' style, which predates the new miniaturized electronics, was almost twice the price for all components.
I left that fan installed (added a second circuit with a pole switch) so I can still use it when 100°+ is encountered, shade is hard to come by, and I am attached to shore power. The trick is to wet a sponge by placing it in plastic pan (Tupperware style) of water set in the lower bay next to the lower inlet. Evaporative cooling is a marvelous way to boost overall cooling in scorching weather. Oh, this only works when parked
The larger fans near the upper vent opening draw air through the entire space, are noisy, and draw considerably more amperage (5 amps) so battery consumption is significant: my design uses the same draw in five hours that the bigger fan uses in one hour. When I mounted the bigger fan, I also built rubber isolator mounts to reduce vibration but it is still noisy enough to be heard throughout the trailer
The fan offering for inside the main cabinet is another older style computer fan and you can accomplish the same thing for less dollars using the same fans I did for the exterior; less noise and less electrical draw again. They do help reduce overall cooling time when you add 'warm' items to the frig but aren't really necessary if the unit is working properly. If you decide to go this route, one is enough.
FYI, both exterior fans are wired to individual pole switches near the hatch opening so I can select whichever I want and when to use them. Neither are necessary under 85° as the refrigerator functions as designed whenever ambient temperatures are below this threshold.