Looking for Digital Thermostat for AC Driven Cold Plates

My boat has a two Grunert AC driven cold plates. Yesterday I noticed that my refrigerator was running to excessively low temps. The last time that occured it was my freezer and defrosting the unit ended up fixing the issue. This time it did not work and I noticed that the original thermostat knob was stuck. I even tried using pliers to turn the control and the plastic knob broke off, also there was a bit of grease that appeared to have leaked from the unit. I am assuming that the thermostat is toast and was told that it would be better and cheaper to get a digital thermostat rather than trying to replace the original Grunert control which would cost around 200$. I have looked on Amazon.com and there are numerous units to choose from all under 20$. Also the current setup has the thermostats inside fridge/freezer. I am guessing I might be able to mount a digital unit externally if I can find a suitable place close by to run the wires?
Has anyone done this and can you recommend a digital thermostat or have any other advise?

PS. My boat is a 2000 Hunter 450 and I have also posted this on sailboatowners.com