RV manufactureres have been making refrigeration systems that run on 110V/12/AND Propane for many years. These systems are cheap and available everywhere due to the high number of RVs around.
Why have I never heard of anyone using propane refrigeration on a boat? I know these systems can last weeks on a modestly sized bottle of gas, which would remove the need for huge wind/solar arrays, Balmar alternators and AGM batts etc etc.
There must be some reason right? I just can't think what it would be.....
Seriously though? What about using one of these:
LP Gas Refrigerator - Norcold 323 on sale - PPL Motor Homes
with all the appropriate sniffers/solenoid etc?