One of our members used to sell leveling systems, I got one of the last he built, that went between the factory valves and the air bag. Mine is wired so the factory valves are enabled when the ignition is on and the manual valves are enabled when the ignition is off.
We've all read, or experienced what running a diesel fuel tank empty will do, at most were looking at 300-350 pounds of change at the front axle burning off fuel. And whatever were carrying in our fresh water or waste tanks, its not going to change until we stop somewhere to dump or take on water.
So my 119-gallon diesel tank holds 868.7 pounds of fuel. A side note: In my trucking days, my boss would always say that we should consider a loss of 1% in fuel economy for every 100 pounds of added weight. That data always seemed exaggerated to me.