One more thought. If your rear springs are too light for the camper and you're relying on air bags to level the truck, that could be part of your squishy problem. The air bags don't help a truck to ride firm and stiff when the springs are already overmatched.
You may need to upgrade to heavier duty leaf packs and/or add a leaf or 2 to the upper overloads.
Torklift Stable Loads will help your overload leafs to come into play sooner, which helps firm up the loaded ride and reduce squat.
If adding 2 extra leafs per side to overloads, you may need to cut down the Stable Loads' height a bit to keep them from coming into contact when the truck is empty.
Heavier main leaf packs is the first step though, in your situation, in my opinion, if you're still running the factory stock main leaf packs. Visit SDTruckSpring.com for heavier spring packs for your truck.