where to measure to determine if trailer is level

We have a level stuck on the side of the trailer and one on the back. They were placed after a level on the floor just inside of the door was level.

Are they perfect? No. But they are close enough. We go to a alot of parks without concrete pads so the lego blocks aren't always perfect either. We actually keep the tongue up a little higher to help with sleeping, since level seems to make us feel like our heads are a little lower than our feet lol.