So I guess that means he will be hauling 10-13K, plus another 6K in truck wight...does that sound right?
Properly loaded 13k tag trailer means about 1,500 pounds hitch weight (11 to 12 percent hitch weight). Figure at least 5,000 pounds for a nice truck camper when wet and loaded. So that's at least 6,500 pounds of weight on the truck, not counting driver, passsengers, kids, doggie, etc.
The Lance model 1191 camper costs over $30,000, and has a so-called dry weight of 3,530 pounds. But ignore that dry weight. By the time you add propane, food, drinks, clothes, and options such as AC and water heater, and with only a splash of water in the fresh-water tank, you'll have a problem keeping wet and loaded weight down below 5,000 pounds.
Lance 1191 truck camper
A 2008-up F-450 pickup has a GVWR of 14,500 pounds, and if it's the popular CrewCab 4x4 it's going to weigh around 9,000 pounds when wet and loaded with passenger(s) before you add the camper or trailer. 9,000 truck plus at least 6,500 payload = 15,500 pounds, or overloaded by at least 1,000 pounds.
So even the F-450 pickup is not enough for that load. He'll need a very special F-550. Ford makes it. Order the F-550 chassis cab with 60" cab-to-axle length, and order it with a pickup bed and 15k receiver added by a Ford ship-thru upfitter. Ford will build the truck with exactly the options he wants, then ship it to the upfitter for the bed and receiver to be added, without increasing the delivery charges. By the time the dealer sees it, it will be a complete F-550 pickup, ready to slide in the camper.
The F-550 can be ordered in XL, XLT or Lariat trim, 4x2 or 4x4, regular cab, SuperCab or CrewCab, same as the pickups except no fancy-dancy King Ranch or Harley Davidson trim. It has a GVWR of 17,950 standard, or 19,500 with the optional payload upgrade pkg. Stock GCWR is 26,000 pounds, but he'll exceed that with a 9,500 pound truck, 5,000 pound camper, and 13,000 pound trailer. So be sure to add the high-capacity towing pkg which raises the GCWR to 33,000 pounds.
With 9,500 truck weight and 6,500 pounds payload, that's about 16,000 pounds on the truck axles. That's a cushion of 1,950 pounds extra payload capacity in case he can't live without the multi-slide luxury camper that will weigh more than 5,000 pounds when wet and loaded. Surely even a former motorhome owner would be happy with a 11.5' truck camper with slides that has a wet and loaded weight of less than 6,950 pounds. So probably no need for the payload upgrade pkg that would handle a camper up to 8,500 pounds without being overloaded.