OK...lets say your camper is a 4500 lb monster like a Lance 1191 or an Arctic Fox 1140 or a heavier Eagle Cap 995. You may get off the pavement to camp but you aren't going to do the Whazoo with it. ...
If 4x4, my preference is General Motors Duramax because it has independant front suspension. Hard to believe Ford is stuck in the 1940's with a rigid front axle.
If 2x4 then Ford gets the nod. Per 2015 manufactures literature, the 6.7L F-350 CC dually has a payload rating of 7080 lbs. That's 1532 lbs better than the like GM which is only rated at a payload of 5548 lbs.
Catch up General Motors...I need at least a payload capacity of 6500 lbs!