I had read that if trailer is over 30 feet then you should use 2 sway controls. Our trailer is 35.5 feet long and I have not had any problems towing in a head wind, side wind about 35-40 miles per hour, 18 wheelers passing or even a real bad tailwind one time.
2011 jayco 33rlds, 2002 Ford excursion, v-10, 3:73 gears 4x4 mine. 2008 Suzuki sx-4, hers. Retired Air Force, now Retired.