When we started RV’ing we soon learned that the typical RV refrigerator could be susceptible to wide temperature variations and not real efficient at cooling.
We learned that it was best to “pre-chill” the fridge, letting it work at cooling down for at least 24 hours before loading it up with food. We also learned that because it is not your typical household compressor fridge but rather an evaporation system that it’s best to put food that has been pre-chilled (from a conventional fridge) into the RV fridge. Also …. DON’T stand there looking for something to eat with the door open! Know what’s in the fridge and what you want BEFORE opening the door – that way you’ll be successful at keeping more of the cold air in the box instead of rolling down onto the floor and your feet.
OK, so we did all that …. but is it really working? We installed a typical round-dial refrigerator thermometer and it kept showing 50 degrees or higher! 
That’s no good. We want to keep our refrigerated food somewhere between 34 and 40 degrees. We turned the control on the front of the fridge to “Coldest”, but still showed around 50 degrees or so.
Finally out of frustration wondering if the fridge was working and if we needed to call a repairman, we installed one of those digital indoor/outdoor thermometers and “voila”, it shows us at a glance what the temp is inside at any time without us having to open the door to look at the grossly inaccurate dial thermometer that we hung on the shelf.
Since buying the digital indoor/outdoor thermometer for the fridge, we’ve also bought another one that I placed the outdoor sensor in the coach basement water compartment. The water compartment has the fresh water supply piping so in that compartment I installed a 60 watt light bulb that is connected to a plug in thermostat that comes on at 35 degrees and shuts off at 45 degrees. Now I can monitor that compartment temperature and be comfortable knowing my light bulb hasn’t burned out and the system is working and I can monitor this from my easy chair in the coach any time of the day (or night)
THIS is a seriously good idea, but where on earth can we get one of these here in the VI???
These are commonly available in hardware stores or Sams Club / Costco, but probably the largest selection can be found on Amazon.com by going there and searching “Indoor Outdoor Thermometer” or just click on this link:
https://www.amazon.com/s/ref=nb_sb_ss_c_1_8?url=search-alias%3Daps&field-keywords=indoor+outdoor+thermometer&sprefix=indoor+o%2Caps%2C316&crid=2LROZKI4NMO7D
If you pay for Amazon PRIME service, (an annual fee) then much of what you order from Amazon has free shipping and the great part is you generally get your order in a couple days without any travel expense.