where to measure to determine if trailer is level

3 things that like to be near level,

1) bed
2) stove top
3) fridge

When we first get a trailer, we level the fridge, using foot long level. We check stove top then, and lay on the bed. When we find the "level" that works for us, we then see what the floor is right inside the door. This allows us to use level right inside door when setting up so we don't have to climb in and out a bunch.