It is generally not advised to run the fridge way off level. The internal mixture (water, liquid amonia, hydrogen gas, sodium chromate) has to be able to move thru the system as designed. The reason it isn't an issue on the road is you're always turning, going up and down hills, and hiting bumps allowing the mix to keep moving and not pool in one place and overheat. The sodium chromate particles in the mix ... when overheated can turn to crystal and start to block sections of internal piping in the boiler. Your fridge gets less and less efficient. This won't happen instantly, but over a period of time repeatedly running off level ... so why invite failure ... level her up a bit?