On my ole 30ft Mirada, I had two self adhesive bubble levels mounted on the wall and the dash. I could usually jockey the coach back and forth or a little side to side and get it reasonably level. If I was on an incline or something and just couldn't get it level, I also carried 8-10 pieces of 2x6 cut to various lengths.. I put a couple pieces under the low tires and that would usually do the trick..
1999 Fleetwood Southwind 35S (Ford F53 6.8L V10 275hp 4R100 4 spd trans) - Toad 2003 Saturn Vue.
It won't do MACH 2, but I can get a sandwich and take a pee.