Before you buy special equipment searching for a solution ,
make sure you have enough tongue weight .
The design of certain trailers and the placement of the axles on the frame of such trailers can be the culprit.
There are ways to mod a TT to cure this, adjustments can be made and might be, money well spent . The most common reason for sway is not a lack of a sway control bar . Least expensive way is , move items in the TT forward to transfer weight. Try that , then road test it .
Adding sway control is helping but not attacking the core of the problem, its just masking it. A strong enough crosswind or bow wind from a passing truck can overcome sway bars if you have not addressed the core problem. Don't be fooled by a false sense of security because you added a sway bar and it feels better in a moderate wind.
Other factors involve the tow vehicles wheelbase, overhang distance from the tv rear axle to the ball .