I don't drop the air when unloading, but since this isn't a big operation, the air is often out of the bags by the time we dump on the trailer with the grain cart.   I mounted the finders so they pretty much sit on top of the tires when the bags are empty and the axles are against the stops.    I didn't change anything on the 5th wheel and think it's standard height.   No problems.   I put fenders on because i was worried about throwing a rock threw the back window of truck.