Never have used a cover ever.
Old style pre-teflon disc was a light film of grease on hitch head and king pin plate.
Thank goodness for those teflon discs!!!!!
Only use a light film of dry lube on moving points of hitch(pivots points and jaw tracts where jaw makes contact with hitch structure) and on king pin/jaw contact points.
Once a year I remove head & mount from truck.........give it a good cleaning and repaint as necessary. Pull the large head mount pin, clean it and the articulating pins. Good heavy grease--reassemble and wipe off excess.