Good response, CycleGuy. Let me add two more things.
Some WDHs also have anti-sway capability. Among them, a trunnion hitch can have a tricky little bend in the springbar tips which, with proper brackets, becomes a "dual cam" sway control. Some info from one manufacturer is here
http://www.reeseprod.com/content/pro...600&catID=1655
Second, it is often stated (and I agree) that a friction sway control is not nearly as good as dual cam.
This is all laid out in the Trail Manor Technical Library - specifically in this article and at least two others near it.
http://www.trailmanorowners.com/foru...ead.php?t=2923
The Library is open to all members.
Bill