Here's the thing with temperature;
All fridge temperatures will vary depending on ambient temp, amount of food and drink in them and how often they are opened. Fortunately unlike household fridges with vertical doors, most mobiles have a lid on top, so don't lose too much cooling if the lid is briefly opened. (Not too often)
Re how full they are; Once what is in the fridge is at the temperature the fridge is set to, it acts like a "heat bank" in as much the food helps maintain the temperature longer when the fridge cycles off. However it does require some circulation of cold air, so "chock a block" is not the most efficient. I find that full with odd shaped packaging leaves enough % space for that. But avoid repackaging with containers to use every last cc of space.
The last item is ambient temp; The hotter it is, the more the compressor will work, the colder it is the less it will work. If I set my Engel to run at as near to 2 C as I can during a hot day, overnight it will freeze. So I adjust it before going to bed. Equally it will need to be re adjusted in the morning.
As I said, my Engel is 23 yrs old, it doesn't have a digital display. I have tried wireless temp gauges, they chew AAA batteries 5 at a time. So I now use a wired Digital gauge, the probe is in the Engel with 1 battery, the display in my centre console. I get about 12mths out of the battery. After years of experience, I've noticed how the temperature can vary at times.
The cover on the fridge is insulated and does help maintain temp as well as protect the casing, as I said it still looks new.
Food safety for refrigerated food (not frozen) is between 0 and 4 deg C. I've found my Engel can vary a couple of degrees above or below where I generally set it. So if I set it at 4 it could go up to 6 before I notice. This is why I choose to set as near as 2 as I can because it's in the centre of the range.
Even so, I check the temp of the fridge at least a half a dozen times a day. When I was in SE Asia in the forces, I got a dose of Salmonella, I've no wish to repeat the experience.