I would go with the air bag. That way you could smooth it out a bit when there is no load.
Also, check the tires to make sure they are inflated properly. If the pressure is low they can allow the truck to feel "mushy".
I'm a little surprised that the truck won't carry the camper as is.
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Stan
93 2WD extended cab, Banks Power Pack, K&N Air Filter, PW Injectors,Auto w/4. 10 rear with limited slip, US Gear Exhaust Brake, 31/2" Exhaust, 5K air bags, Boost/Pyro/Tach Gauges, Green/Silver, 146K