I have an 08 Duramax 2500 with the 811. I have airbags and 19.5" tires on it.
I Went with 19.5 cause of safety reasons. Overall the truck will carry the camper ok, it is not a perfect setup by any means. I would suggest doing something else to the suspension as I have air bags and to this day don't really like the way the camper fits. I have had the camper about 8 years and have put about 40K in miles with it.
The biggest problem I have and am concerned about is the brakes. The thing warps rotors like crazy. I have even bought some pricey ones. I weighed the camper once and it wasnt 100% loaded with gear but the weight sure made my eyes open. Hence the Tires.