I'll appreciate hearing other opinions on this also. But if I'm thinking correctly, I wouldn't worry about going down. As your truck heads downward, the WD bars would tilt upward, and remove stress from the hitch. The trailer would follow, limited only by the radius and coupling of the ball hitch.
On the other hand, when you leave, and begin the rise up the hill, the WD bars will pull down a little on the trailer. If you want to avoid that, just pull it up the hill without them, and attach them once you're on the level street, and off of their drive.
What about it guys? Am I thinking right or wrong?