Either a F450 or F350 will carry a truck camper. In some years, the F450 with 4.30 gearing is much more capable of high loads and has bigger brakes. You can find the towing guides here.
http://www.fleet.ford.com/towing-guides/In the 2017, things seem different. It shows a truck camper payload of 4510 for the F450 vs 5010 for the F350 crew. Also, only a 700 lb advantage for the F450 for fifth wheel towing.
It would be interesting to see the difference in how the 2017 F350 vs F450 turns, but otherwise, they are pretty close. The 4.30s will probably still tow a bit better, but at the cost of MPG.
Assuming the deals are still better on the F350s, I think looking hard at the F350 makes sense.