Air bags help with the springs. They don't do a thing to help the tires, wheels, or axle bearings. Your axle weight on your door sticker is with the tires listed on the door sticker. Your wheels will also have a weight rating (hopefully larger than the one on your tires). Your rear axle MIGHT be able to carry more weight if the tire and rim capacity is increased. It's hard to say, you'd have to find out what the real limits were on the axle. As an example, the rear AAM 11.5" axle in my Chevy Dually is rated on the door sticker for 8,500 pounds but AAM rates their axle for 10,200 pounds. I don't know who made your axle.
So again, weigh the rear axle loaded for a trip. If, for instance, you have 6,000 pounds on it and the tires are good for 2,700 each then you have a problem. It doesn't matter how many air bags, timbrens, etc. you install.