Yes, I have a cover on mine and that keeps most of the weather out but, it still show rust., never been a problem, just wondering. I shall continue the use plenty of the brake cleaner.My Westfalia detachable towbar came with this
When i detach my towbar i put this in the hole
it stops anything getting in..
Our Tow Trust has a cover that clips over the opening so no issue. I remove the towball every time we are finished towing even if only stopping for 2 nights. No shin banging and blue air.My Towtrust is specific - NO LUBE! I have a removable because the drive is short and I'd dent the garage door every time, I remove the ball every time, and replace the cap. I had difficulty getting the ball to engage first time this year (about 3 weeks ago) and fixed it by wiping the socket out with kitchen roll