12v is not free
The 245w heating element will draw have an inverter draw of over 20amps
That power has to come from the drive engine turning the alternator
The fridge uses very little propane
The cost of the propane used will be less than the cost of the gas used to create the power coming from the alternator
As far as safety, I used a propane fridge on l.p. for 16 years straight, never on electric , always propane moving or parked, only turned off during lp refill
This RV has a residential 120v compressor fridge
But that is another topic