I do what the Pullrite manual says to do. WD-40 on tubes and everywhere else the manual states to apply a WD-40 like lubricant. Sometimes I wipe a small amount onto the plate, more for corrosion control that anything else. I always wipe it off if I apply it to the plate. Just leave a shinny coat. I try to apply WD-40 every time I hook up when I plan to travel a reasonable distance.
2013 Ford F-350 SD Diesel, 4X4, Crew Cab, Lariat
Sabre 2014 32RCTS, Pullrite Superglide 2900 18K