It's true that the trailer can be slightly out of level without harming the fridge, but I am one of those ultra-cautious folks -- why take a chance?
So because our driveway has a definite slope, I always level the trailer as best I can when we park it. If the driveway is level side to side, leveling the trailer is easy -- just use the jack to move the nose up or down.
If the driveway has a "right to left" slant, you could use Lynx blocks -- we call them "giant Legos." Or just a piece of wood of the right thickness. Pro tip: cut a slanted edge on the board so that the tire can ride up the slant onto the flat board. Otherwise, the board might just scoot down the driveway when the tire hits the square edge.
Don't ask how I learned this.