We have a 27' class C without jacks. In our travels to music events and the like, we have been placed in some very off-level spots, with no chance to move, so we must be ready.
We have a Level Mate Pro, which is my favorite accessory by a large margin. We also carry six packs of Camco yellow blocks. It's a very rare situation indeed that we can't get within an inch of perfectly level. I've had a corner of that rig up on on over 10" high pile of blocks more than a couple of times, with no trouble. And, with the Level Mate Pro, it's rare it takes more than one shot to get it perfect - only the worst spots sometimes require a second attempt.
With this system we've received plenty of compliments from bystanders when they see how quickly we get level, even on challenging terrain with a ridiculous pile of blocks on the ground.