Fortunately, it's never been an issue. Most sites that we've been in were very level. In the few that weren't, we were able to move the rig around a bit 'till we got it to within a half bubble, which as all you need to keep the fridge happy. If we ever do run into an out of level situation, we keep a few boards with us to take care of that situation.
Remember, the only important thing that you MUST keep level is the fridge. Just put a bubble level in the freezer compartment, and level to that (at home). Then put a second bubble level on the dog house (or any place that it's easy to see from the drivers seat, and shim it level and glue it down. From then on when that level is within a half a bubble, you'll know that you're good to go. You won't have to level to the fridge again, as the level that you put in the cab matches the fridge level.
Generally, when we pull into a paved site, the level is almost perfect. When it's a rougher camp site, we just move the unit a foot or two in one direction or another till the level in the cab shows within a half bubble. Really pretty simple...
Good luck and safe camping!
2016 Redhawk 26XD
Me, Dear Wife,
2 Bluetick Hounds
1 Newfoundland / Black Lab Mix
1 Cairn Terrier