Yes we have a Thetford fridge and it seems to work ok .
I never mess about getting van really level as mainly wildcamp and just use the lay of the land and
shunt about a bit until it feels ok .
Cannot be bothered with all that messing around with ramps ! Lol If I wanted to mess about I would buy a caravan .
I would guess yours selects its power source automatically ?
What settings are you using ?