raschemmel:
You would use an accelerometer.
Why ?
Can you show some documentation that says it provides leveling ? (because I haven't seen it and if it exists , I would prefer to know that , than not.
It is a standard use case for an accelerometer. An accelerometer with a sensing axis exactly horizontal will read zero but in this orientation it is highly sensitive to small deviations away from horizontal so it makes a very effective tilt sensor. This technique only works when the accelerometer is at rest (it is no use on a moving vehicle), but I would expect the camper to be at rest in this case.