FIredog,
WD is shorthand for weight distribution hitch, allowing for more evenly balancing the tongue load of the trailer across the front and rear axles of your tow vehicle.
While you didn't bring up sway control on a Bambi, take a look at this thread for some discussions on sway control and weight distribution:
http://www.airforums.com/forum...rol-17986.html
You'll find many good discussions here and I'd encourage you to use the search tool to browse for varius topics, and don't hesitate to post simple questions.
Finally, if you haven't one already, I'd strongly recommend that you find an experienced travel trailer dealer whom you trust near your home. They can be invaluable in helping you through and saving you money.
Good luck,
Marshall