Best way to level your rig?

Thanks.... the countertop seems to be a good place because doors, etc in my rig seem to follow it instead of the floor. I thought the floor was the better place because it's tied directly to the frame that everything else is tied to but things seem a bit off kilter .. if you know what I mean. I was wondering if there is much flex depending on the terrain that might give false readings. My plan is to drive to a flat parking lot like our local high school and attach leveling bubbles so that leveling in the "wild" is a little easier. I appreciate the reply.