Just traded in my 2011 F350 in September.
Now that part is irrelevant, other than to show I did own one.
Yes, the camper package is for truck campers in the bed/box of the truck.
I did not have the camper package, it was a dually. I even had the dreaded slip of paper in the glove box saying my truck was not recommended for hauling a truck camper. I did have the factory rear stabilizer bar.
However, hauled the truck camper in my signature, over 4,500 pounds wet weight, all over the place without problem. The ONLY change ever made was a set of upper StableLoads, which allowed the overload springs to engage earlier than normal (they are over-sized rubber blocks which replace the factory small rubber blocks in those positions).
So unless one is planning the truck camper route, you can get by, as I did, without the camper package.
Go for the 20 inch wheels as you like them, so get them. However, be aware as for load capacity of the tires to haul a load, the 18 inch and 20 inch can both have similar capacities.