Also too, what type of Six Pac camper are you thinking of getting? I have a 91 model 78S that fits in the back of my 65 Chevy short wide. I had to make a 2 inch spacer (flat 2x4 with 1/2" ply on top) to put in my bed so that it would have enough clearance to allow truck flex. Without it, it sat within 1/8 inch of the roof.
I replaced the stock coil springs in the rear with HD overload coils. Also, added air shocks. The truck handled the weight before without problem, but I always like to over think things...Now I KNOW it will handle the weight without problem.
Just saying, don't go too big on the camper (the Six-Pacs aren't light) without considering the truck as well.