Re: 3.5 cu. ft. chest freezer with thermostat as a refrigerator
Typically, the freezer thermostat will not go warm enough.
Also, sometimes they don't work very accurately at that end of the range (you want to fridge somewhere between 33F and 40F (you may not find a setting that stays above 33F and does not go above 40F)...
A freezer that is set for 0F and cycles +/- 5F is not a problem. A thermostat set for 37F that cycles from 32-43 is probably not desirable.
I assume you will be running this off an inverter... You will probably want to pick an inverter with a DC inhibit input so you can cycle the inverter on and off with the thermostat mechanical and save the ~6-8 watts of stand by power. Or you can pick a DC powered temperature controller (low power draw) and cycle the AC or DC (you can use an inverter that has a search mode that only draws more power when there is a >8 watt AC load)...
20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.