I have a F350 camper certified that originally had airbags. I think the major purpose is to level out side to side sag (one side heavier than the other). They don't seem to help the ride at all.
I added Stablelifts and Bielstein shocks, and they greatly improved the bounce in the ride, but still have problems on older concrete roads with seams and on some bridges. Still keep 90 psig on one side and 40 on the other. After reading the above, will try deflating them to 10 psig and see if it affects bounce.
The 08 350 4WD dually has a rear sway bar, and it looks like Helwig doesn't make an upgraded one for that model.