How critical is it to have a perfectly level trailer?

Use this type bubble level for refer leveling. Put it on the freezer floor. If the bubble is outside the center circle, your refer is out of level for correct operation. UNLEVEL operation IN TRANSIT, is OK as the movement negates out of level problems. BUT, people forget those time they stop for a few hours or overnight and leave the Trailer connected out of level. If that happens, you just shut the refer OFF. Then restart when traveling again. Doug