Suggest you use wireless thermometers, they work great and are accurate.
https://www.acurite.com/media/manuals/0 ... ctions.pdf
I have used these units for both refrigeration, freezer and engine room monitoring. Cost is under $40 with one monitor and two sensors. They also have alarms and measure temps from -40 to 100F. It is important to use Lithium batteries for the freezer sensor. It does require pairing which takes a little patience to get it right if you have two monitors.