The camper package is of no significance on the diesel F350 because it already has the heavy front axle and rear stabalizer. The 20" tires are rated for more weight than are the 18" tires. (3750 lbs per tire for the 20" and 3640 for the 18" tires) The 20" rims will give you a little more "stability" due to their lower profile. 20 wheels also provide for a little lower rpm at highway speed if you are getting the 3:55 rear end. This lower rpm will equate to a little better fuel economy. If you want the best fuel economy you need to go to the 3:31 rear axle ratio which will require you get 18" wheels.