The RV must be fairly level for the refrigerator to operate properly. Older RV refrigerators required more precise leveling, but even the newer models need to be close to level for optimum performance. Over time, a cooling unit operated out of level will be permanently damaged.
Traveling with the refrigerator on will not cause problems because the liquids and gases in the cooling unit are constantly moving around. They don’t collect and stay in areas of the cooling unit like they can in a stationary, out of level refrigerator.
The initial cool-down process can take four to six hours. You should turn the refrigerator on the day before you plan to leave, and before you put any food in it. When you do load the refrigerator the food you put in should already be cold, and the food put in the freezer should already be frozen.