I can sit in the driver's seat of my truck and tell, really close, if I'm level.
I'm a level idiot savant, I reckon. And an excellent driver.
Dang sure close enough to spend a night. If I am going to spend multiple nights, i may refine.
The only aspect of level which is critical to me is that my head cannot be lower than my feet in bed. Not even by a half-inch.
My resourceful amazing self can even deal with that though!
I just gather up my pillow and carry it to the other end of the bed.
I used to use an 8" level to dial in for a multi-day camp, but I recently picked up a little square omni-directional level and stuck it on the kitchen counter.
It is annoying. Accurate but annoying. I just don't need to be that level.
Joe