Couple things..
Keep the fridge side of the camper out of direct sunlight is possible
Install a second fan blowing up and out the overhead camper vent
Refrain from opening the door to check interior temperature, get a remote thermometer (10 bucks at Wally-World). Ammonia fridges will always have recovery issues when you open the door a lot.
The only time I open mine is to remove food or add something.
Check the cavity space around the fridge for adequate insulation and add insulation if it looks even slightly sparse. Unfaced kraft R12 is 8 bucks a roll at Lowes. Stuff the space with insulation on all 5 sides (bottom too).
On a top (roof vented fridge, no baffle is required at the top. Thats only for a side vented fridge.
Finally, add an interior cooling fan to move the air inside the fridge. The warmer / colder air inside stratifies. Moving the cold are inside the fridge will hep cool it. (Available on Flea-Bay for less than 20 bucks).