Brian Reay laid this down on his screen :
Virtually motorhome Ive looked at has a three way fridge, gas, 12v, 240v


I have seen gas/240v only, but the more desirable ones are the 3 way
fridges. They run most economically cost wise, on 240v.

240v and gas use a thermostat, the 12v does not - they run flat out
continuously, barely able to hold the temperature down.