Not addressing the original question, but I'm another one who had trouble with the trailer on downhills, it fishtailed horribly, and ultimately caused a terrible crash. I had really weird/bad handling - big uncontrollable swerves - over about 20 mph.

I switched to panniers, and love how they make the bike feel like a normal bike, only heavier.

I guess that goes to show there are a lot of factors that affect the bike handling - I think one big factor for me is that I'm quite a small person, and was riding quite a light bike, with a fairly heavy trailer. I think BOB is officially rated to 30 pounds and 25mph, I exceeded both and had serious trouble.