Mmhh, we don't have a temperature gauge on our Engel MT 27F at all. It is continuously adjustable on a scale from 1 to 5 with a wheel. It has a temperature range of +5°C to -18°C, which is about 41°F to 65°F. I usually don't set it higher than 1 on the scale, because otherwise the inside starts to freeze.
The fridge, like many others, has a practical inner basket. Such baskets are also available individually. Thus, the fridge can be easily packed (e.g. from the house into the rig and vice versa) and the contents can be removed completely easily - such as for cleaning - the box. For packing inside, we like to use such small leak-proof plastic boxes for individual things. Then everything is not lying loose in the fridge and can be removed more easily. With this you can also sort things thematically and everything doesn't tumble around - especially when it gets rough on dirtroads.
We always make sure that the fridge is well filled, because, also the contents of the fridge acts similar to a cold accumulator. Beer cans are well suited for this - hahaha. So the fridge does not have to cool down the air inside.
We have an ARB 63 qt fridge. After calibrating it and a week or so of experimenting with a thermometer, I settled in on a setting of 38 F. I place a towel, cut to size, on the bottom, below the rack. Meats and cheeses are packed in the bottom along with other liquids and veggies up top. All fridges are different, so use a thermometer and fill it with cans/bottles of liquid so you can establish a baseline.
I keep from 32-39. It all depends on the state of my battery pack and what my plans for the next couple hours are. Examples: driving, set to 32. In camp with perfect sun pushing 75+w to the battery, set to 32. Bed time or cloudy days I bring it up to 39. All about battery management and the current conditions.
Every fridge is different. First calibrate your fridge display (if it has one). Start off at 37 degrees at the lower section of the fridge (fridge at least 2/3 full). All fridges have temperature swings. Eco mode will typically swings more than regular mode. +/- 2 to 3 degrees is typically. So 37 degrees can take you down to 34 degrees. Any lower and you'll freeze precious vegetables if they fall to the bottom of the fridge.