This is what I had when I was towing a caravan, also using weight-
distrubition bars:
http://www.hitchesonline.com/sway.htm

It connects on the side of the "V" of the trailer tongue, about
2' (60cm) back from the ball, and then on the hitch side, about 6" (15
cm) off-side of the ball. The amount of friction can be controlled to
reduce the swaying movement of the trailer.