After some more thought, that camper over the bed configuration has to weigh 2500-3000 lbs. If the payload rating for the whole truck is only like 2800 lbs, how is that safe or certified by Ford? Add a few humans and their belongings and the truck is definitely overweight, despite being used for its intended use.
Do you really suspect that Ford will sell you a product that takes your vehicle beyond it's operational GVWR? Because i seriously doubt that.
Companies like RAM won't even let you get a sunroof with certain combinations because it puts them too close to GVWR.
For short beds they range from 2,100 to 2,900. Short bed trucks have higher payloads as the truck doesn't chew up as much of GVWR.
With the HD Tow Pack a regular cab 2WD trim with the 3.5 EcoBoost F150 will do north of 3,000 lbs payload in the bed.
Even so all configus of F-150 have a 6,000 lb or so GVWR, so your concerns are non existent
2016 Ford F-150 | Payload Specifications | Ford.ca