If you're getting pushed off the road by passing trucks or lines of cars, that is NOT sway. You can install both a DC and dual friction bars together, and it will not solve the problem.
Sway is when the trailer wags back and forth uncontrollably behind the truck. A single oscillation is not sway. A side-to-side bobble from uneven road surface is not sway. The whole rig moving sideways as a single unit is not sway.
Unfortunately, I don't know what the solution is, but if the rig isn't swaying, then sway control will not solve the problem.
Sway control is still an EXCELLENT idea, but for other reasons.