The only critical components for leveling are your refrigerator and any slides. The reefer needs to be within a couple of degrees of dead level to keep the coolant from crystalizing - and once that happens, you buy a new reefer. As far as the slides, check your user manual. But if the rig is level enough for the refer, it's gonna be level enough for the slides.
We use a bullseye level on the kitchen counter and try to get it as close to dead center as possible. But if it's leaning a bit one way or the other, long as the bubble is withn the bullseye, we figure it's good. And if it tilts a hair toward the back, the AC runoff will go behind the slide.
al