You do not need a adhere or sway bar, UNLESS you have trailer setup incorrectly. You should be able to tow your trailer with out bars etc. If you need them to tow safely, you are towing an unsafe trailer. Fix issue, then put bars on.
The biggest issue I noticed pulling my TT with vs without. My rocked side to side more with crosswords with no bars, less with a WD system, less yet with a dual cam.
The only time I've had uncontrolled side to side movement like a fish tail moves, was when the trailer was loaded incorrectly. Usually, too little hitch weight. A 12k lb truck, will not stop a 6000 lb trailer from swaying! I can say this from experience!
My 02 on subject...
Marty