Ford does the same thing with even their F350 dually pickups. Really. Unless you order the camper package you get that piece of paper/sticker that tells you the truck is not rated for a camper. If you order the camper package option on the same truck, then you'll get a piece of paper that tells you how much camper weight you can handle based on where the CG of the camper sits. Depending on what other options are on the truck, you may already have all the parts that are part of the camper package.
So I wouldn't be too worried about the sticker. I would be worried about whether you are overloading the tires and axles (especially axles on a 1/2 ton truck that probably doesn't have full floating axles). And if the truck handles horribly with the camper loaded, then you'll probably need to upgrade the suspension. If you read some of the old posts you can find some good info on suspension mods.