The cooling vanes in the top of the food cabinet are responsible for simply convection cooling the air inside the fridge which will tend to drop into the bottom of the cabinet so the 'D' cell battery fans fans you are hearing about simply help to push that cooler air around the food items in the fridge to help equalize temps throughout the cabinet.
Air is the worst item to try and cool so an empty or only partially full fridge is going to work harder to stabilize itself at colder temps.
Some easy-peazy steps you can check before spending a lot of money.
If you are good with a volt/ohm meter, the thermistor clipped to the vanes should show a specific range of resistance measured in ohms and if you research that (I've forgotten so verify please but 8500 ohms rings a bell), you can check it by putting it into a tea-cup full of hot water to observe resistance readings changing with the meter.
The termsitor reacts to warmer air by changing it's resistance as it warms up to trigger an "on" so therefore the higher up on the vane into the warmer area at the top of your food cabinet, the more frequently it should cycle the heat source to your fridge boiler to come on.
If your fridge is installed in a slideout, the air circulation has to make two right angle turns as it enters the rear outside bottom grill, rises up past the cooling fins of the transfer unit at the top pf the fridge and then exits out the upper outside grill, this is less efficient than a fridge with a roof mounted exit vent so sometimes fans are installed in that space behind the fridge to accelerate convection air moving up the rear of the cabinet. The trigger for that/those fans will be a pot (about the size of a nickel) mounted to one of the transfer coil fins with sheet metal screws at the very top of the rear of the fridge inside that upper outside grill.
That pot will likely be marked with it's 'temperature on' rating and will likely be in the neighbourhood of 130-140F. This can also be checked using the same method with a cup of hot water and ohmmeter to see if you get continuity across the leads after you heat the pot up to it's rated temperature.
These evaporative brine solution fridges work well for a time but can very suddenly simply start to fail for a variety of reasons with very little control by you to prevent it.
Propane operation is the most efficient heating source for the boiler BUT the exhaust from the propane burner at the very bottom of the fridge goes up through a chimney tube in that same cavity behind the fridge so if parked with direct sunlight on that side of the RV you can only imagine what kind of temps the rear of the fridge is experiencing.
A 12v pancake fan, preferably two, mounted about halfway up that cavity aimed upwards will make a huge difference in the amount of cooler air drawn in the bottom grill and over that transfer coil at the top of the fridge along with helping to push out the exhaust heat from your propane burner heating the brine solution. Any DIY handy person can mount two of those on a circuit pulled from the fridge circuit board 12volt supply and protect the board with a 3 amp fuse with that aforementioned pot mounted to the fin at the top in series with the fans. That will make their operation automatic and also protect the board.
