All ammonia absorption refrigerators (RV refrigerators) have to be level, when stationary and turned on to any heat source, period. Not doing so will permanently damage the cooling unit. If stationary, on, and out of level, liquids in the cooling unit pool in places they shouldn't and cause the boiler to overheat and plug or crack.
All refrigerators, except the Sibir, need to be leveled on the freezer plate (if present) or the freezer floor, if there is no freezer plate. Use a round bubble level and level the RV so that at least half the bubble in the level is inside the circle. The Sibir, which has a slanting freezer floor, is leveled on the bottom shelf of the refrigerator.
Traveling with the refrigerator on is acceptable, since the liquids in the cooling unit are sloshing and not pooling.