Regardless of device you use, you still have to determine "what" is level in the camper, that is most important? The inside of the refrigerator? The stove top (so eggs don't slide out of the pan)? Counter tops? The door frame? The floor? The Bed? The air conditioner? The holding tanks? Because .... I've never known an RV yet that will have all of these things level at the same time. A carpenter's level is still the best. It doesn't depend on electricity and is always accurate. I level mine based on the entry door frame, front to back and side to side. Works every time. If the entry door is straight both ways, and there's no swing in the door, everything else is pretty close. At least it's in good alignment with the stove top, and eggs don't roll on the floor on the counter tops! And the water standing in the bottom of my toilet is pretty level.
