First off, Ammonia fridges don't slowly die. they die from the ammonia solution leaking out from corroded piping and if they 'spring a leak', you'll know right away because one, you will smell it and two, you'll see it. The solution as it leaks will leave a yellow stain (usually around the lower part of the boiler, which is the sulfur in the refrigerant solution. That is a rare thing.
Just listen to Mr. Biscuit he knows.
Air flow across the upper evaporator (on the backside of the fridge) always improves efficiency. The unit has to get rid of heat before it can cool and that applies to all fridges, not just an ammonia fridge. Airflow, proper insulation and keeping the door closed and using a remote sensing thermometer (instead of opening the door all the time to check the interior temperature) all work toward keeping the fridge cold.
Ammonia fridges don't recover as quickly as a compressor fridge recovers, Keep the door closed as much as possible.
Interior temps below 42 are fine for food. They are not impacted by changes in elevation at all. They are impacted by external heat like the sun shining on the fridge side of the camper, especially with no additional induced air flow.
People tend to ignore the fridge until it fails and failure (besides the control board) is usually caused by a fouled from dirt or bug poop burner orfice and/or a sooted up boiler flue caused from improper maintenance. All ammonia fridge's that use multi method heating of the boilers (propane / 110v / 12 volt) have a removable flue baffle in the boiler accessed at the top outlet (of the boiler). It's removable and cleanable. I bet 99% of campers don't even know it's there, but then 99% of campers never bother to read the owners manual until an appliance don't work correctly and then they may (or may not) read it. Why bother when you can get online and ask and someone will answer. Everything you need to know is in the manual that came with the appliance. Reading comprehension is poor today....lol
Mr. Biscuit knows. Just abide by his comments.