Please keep in mind that helper springs or air bags or adjustable shocks will improve slightly the handling of the rear end by stiffening it a bit but they do NOT really do anything but raise the rear of the body above the rear axle
to give the appearance of a level, unloaded vehicle.
They do NOT increase the weight
or towing restrictions of the vehicle and the do NOT move any of the cargo or tongue weight
to the front axle/wheels/suspension. You could actually get the same effect by jacking up the rear end and inserting pieces of 2x4 between the springs and frame...