While various of my other senses are deteriorating with age, my sense of what's level seems to be hanging in there. When I pull into a camping spot where it's theoretically possible to be level, I go by feel. Pull a little forward, a little back, a little left or right and... that's close enough. No boards or ramps under the tires.
If I need to compromise, I go for the rear up a little and tilted a bit to the driver side. That keeps blood from running to my head when I sleep, and it has me rolling toward the wall rather than off the bed.