A 5000lb truck camper with the COG 6" behind the rear axle has the same effect on the front axle as a 500lb tongue weight on a ball hitch at the receiver. In other words, not even noticeable.
For the COG of the camper to be making the truck of the front end "light," it would have to be near the rear edge of the truck bed.
I really don't think what you felt was the front end "getting light." Duallys have very stiff suspensions, and they will launch you into space if you hit a bump hard.
I once made the mistake of rolling over a speed bump at more than a crawl with my empty dually, and threw my back out.
It would behoove you to SLOW DOWN when you anticipate hitting a significant bump, rather than just charge over it at speed like you would with a softly-suspended car or half ton truck.
