Friction anti-sway device use in rain or wet roads

It is as Burbman stated above. That said, I used a friction sway control for many years before purchasing my Hensley and never once loosened it up for rain or pulled over to adjust it. The few times I towed in snowy conditions, I did not use at all. Never had a single problem with understeer with it on. It may well have something to do with how well your WD hitch is adjusted and how much weight you are putting on the front axle of the truck.
Barney