In the TT we leave some things in the refrigerator. It is a absorptive two-way which uses 120VAC when available and propane/12VDC if AC power isn't available. We leave the TT at a site unattended sometimes for a couple of weeks. But we don't empty the refrigerator and it is in the AUTO mode. We take all meat items or high spoilage stuff out when we leave, but condiments, bread, peanutbutter, soda, wine, frozen veggies, cheese, etc. are left cold.
We are counting on the refrigerator switching from 120VAC to propane/12VDC in the event of AC power loss. That has worked fine and will work as long as the battery and propane are available. However, there is always the possibility that something will go wrong.
We use a simple memory thermometer for the freezer. We filled a 3 ounce plastic cup with water and placed it in the freezer. We also placed a quarter in the freezer. This prepared the thermometer.
Several hours later, we removed the frozen cup and quarter. We placed the quarter on top of the frozen water. Then we put it into the freezer.
If the freezer begins to thaw, the ice will turn to slush and the quarter will sink into it. On return to our TT we simply check the freezer. If the quarter is resting on top then we know the freezer temperature has never warmed above 32F.
