If you dont want to do a real bag setup then you should look into getting some more leaf springs in the rear. I would bet you could find some heavier springs for that truck or weld in a helper coil spring going from the axle to a custom bracket on the frame.
Springs can be ordered easy just look around
I dont know what effect the bags would have staying inflated all the time, you would need a tank as you need to have the air able to have a little bit of movement, if not it would be like sitting on a baloon and POP!
a small tank, bags, compressor, brackets, and lines and fittings is probably gonna run you close to $750 or more...or there are companies that make "helper" bags some guys have used them on thier astros you could try looking in summit for them too