We keep ours as level as possible most times but I don't overthink it as these later model RV fridges seem more tolerant operating under un-level conditions.  When trying to catch a few hours of shut-eye overnighting at a retail shopping center, truck/rest stop, casino etc. we just find a relatively level spot, and if we have to drop a board or two to get closer to level we just do it, no sweat.  We are never perfectly level as we also like to sleep at a certain angle and allow for rain run-off as well.