An old F350 long bed won't need any suspension upgrades to carry a small TC with ease. My 92 F350 Crew Cab long bed had seen as much as 6,000# of dirt (nothing like paying $10 for a truck load and hauling out 3 tons, overloaded but short runs home) and easily carry a 3,000# truck camper. Truck weighed 6,800# with a 9,900# GVWR leaving 3,100#, going on GAWR adds up to around 11,000#.
Tie downs can be fabricated for under $100 combined with chains and turnbuckles. Not the norm for today, but worked for years on older campers without problems and still would work today. Though adding some cheap spring loaded happijacks bought used for $100 also works. So still have close to $20k for the camper.
Should be able to get a nice camper for $8k leaving a nice $12k for the truck. Five years ago I only paid $6k for my 2004 815. So I think he is on the right track for a good reliable setup.
And yes, take jefe up to your claim. He would love the trip and you can see how his rig handles the roads. There had better be a trip report if y'all do.