Like Boyd said, it really isn't critical. Besides feeling awkward or intoxicated, being too far off level will affect slide operation, and force the fridge to work a bit harder. A single lego needed is only a one inch variance, over an almost 8' wide span, slightly more than a 1% variance. I've been forced to camp for a week at a time worse than that!!
2014 RAM 2500 Laramie 4x4 Quad Cab w/Cummins Turbo Diesel, 2009 Rockwood 2607, and 3 'yaks!
300W of Suntech Solar, a Rogue MPT-3024 Controller, and a Xantrex PW2000 Inverter