geusterman,
The amount of "squat" you get with the camper in the bed will not change, however, with the factory (~4. 75") spacer blocks, the forward rake is much greater than it appears. How is the stance of your truck, with the camper in the bed? I'll bet it still sits slightly higher in the rear. Unloaded, my truck still has a slight forward rake with the ~2. 25 shorter spacer blocks - it now sits about 2 inches higher in the rear (measured at the axle centerlines). I don't know how much weight it would take to compress the rear springs 2 inches, such that the truck would sit dead level, but it would be quite a bit, probably not 3500 lbs. though. It may not be too bad if you were slightly nose high with the camper on board. You could measure how much squat you get with your camper, and calcluate how much shorter spacer blocks you could tolerate.
I have parked next to several Ford Superduty's, and my lowered rear truck has an almost identical stance to the fords... they do not have near the forward rake of the Dodges, the front height is about the same, but, in stock form, the Dodge is waaay higher in the rear. If you lowered your rear end a couple of inches, the stance of your loaded truck would probably be nearly identical to a similarly loaded F350.
Another possible option, if the lowered truck sits too low would be to add an additional spacer between the main spring pack and the overload spring to make the overload engage quicker, and reduce the squat. Airbags would be another option.