I've towed everything from an Apache Scout (very small tent trailer) to 5th wheels and travel trailers over 30 feet in length since 1962 (yes, 1962) and have never had any sway with any trailer nor any tow vehicle, all without an anti sway device. That's over 50 years of towing experience in 49 states and several Canadian provinces and territories. I see no need for an anti sway device provided your trailer is properly loaded and hitched. That said, those devices are not very expensive so, if it makes you feel more secure, get one.
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