If you live in a regular stick or brick house or apartment, there are certain things you expect and take for granted. If, for example, a door does not stay in whatever position you leave it in – halfway open, or just slightly ajar – you assume that there is a problem. Maybe the floor is not level, but more likely, the door is not hung correctly on its hinges and an adjustment is needed. But if you live in a motor home or camper, a swinging door means something else entirely – it is telling you that you're not on the level.
Of course, in an RV there aren't a lot of doors that this can happen to, which is a good thing for the whole process of leveling. In our older motor home, we only have one door on hinges – the bathroom door. In larger RVs there may be other doors to deal with, but you really only need to pay attention to one to make this fun method work. There's not that much to it, naturally, if you think about it. Assuming that when the rig is level, the door stays where it should be, then if the door swings you can assume that the rig is definitely not level. So, you adjust the camper's leveling jacks and stabilizers until the door stays put, without a bungee or a doorstop. When that happens, you can be sure that you and your home on wheels are on the level.
In addition to swinging doors, another fun way to tell if your rig is sitting level is to observe the mood of your cat. Clearly this won't work if you don't have a cat, but for ours whose litter box sits inside the shower stall - yep, he yells and screams if the door has closed shut, blocking his entry to the bathroom. And if the swinging door closes after your cat has gone into the bathroom, you may as well give up and use some other method to get level. After buying your cat a present and apologizing to him, of course.