Good thread with lots of opinions--one more vote for WD simply to put closer to unloaded weight back on the front axle. There is no need to put more, but design weight will tend to reduce over steer that might be propagated in a sway situation. I tow with an F-350 so I sure don't need to worry about the rear suspension in my setup.
Safety and preventing sway is a fuzzy issue--each has his/her own minimum, but you want to be as safe as possible because sway is dangerous. After a sway that took him across 3 lanes of highway, my son changed from thinking that he needed no WD or sway control on his diesel F-350, dually, crew cab, long bed, truck to using it every time, even with a light camping trailer. Yes, something was wrong with his setup or he wouldn't have swayed, but all he found was a tire down--he had been careful to front load for proper tongue weight. Some type of sway control is advisable to dampen things down if it gets started. Yes, modern Ford 4 wheel trucks have sway control that reacts after sway is detected but why not put some additional sway control in the hitch setup. Sway can kill.
