Do I Need to use a WDH with an F350 SRW Powerstroke?

When my truck was loaded up at 12,000 lbs and I was towing 8,000 lbs, I did not need sway control for my enclosed trailer. When my truck was loaded up at 9,000 lbs and towing an 11,500 toy hauler, I did use a friction bar. I think it depends how heavy the trailer is verses the tow vehicle and how much surface area is on the trailer - This is why you will get so many varied results. Sway control will not hurt, but you may not need it for a particular combination.