Bag it and go for it. Running a few 100lbs over GVWR won't hurt a thing. Not that I'm in the right or anything but I'm running 200lbs over my 9600 GVWR and can't tell a thing. I too have a 2500 albeit a Ram. Only difference is spring pack. I'm well under my RAWR, tow rating and GCVWR. If you are too then bags would be the ideal way to go. I honestly sometimes forget the 5er is back there, especially when on a long trip down the freeway. If being over by a couple 100lbs means something drastic will happen then I'm still waiting to feel it. Been running 3 years this way and wouldn't change a thing.
Just curious, why do you think you need bags or something? Is the rear sagging real bad?