Your problem with swaying is the result of a problem in manufactureing ,and that is the "A" frame . I would almost guarentee that the process of making the "A" frame is a complete one in that the whole frame is made in one piece and then attached to the chasis when the plate for the ball joint coupling should not be welded on untill it has been aligned with the chasis .
A simple test to try is to place a straight edge across the a frame as far as you can to the front of the frame then get down on your knees if need be and line the straight edge up with the first cross member of the front of the main body of the van , if you are having trouble with snaking or swaying the straight edge and the cross member wont line up .
What you need to do is free up the coupling plate get a crow bar into the a frame and line the straight edge up then weld the plate back on then tow at 100MPH if you are so inclined , I have fixed the same problem in a number of trailers by doing this without fail .
Hope this will be helpfull and save you money buying anti sway bars you dont really need .
Cheers Bob
Bob Brand ., April 2010