I use a heavy duty ball that is not even chromed. It gets rusty at spots after I wipe the grease off in between trips....no big deal. It is just surface rust, and will that will wear off during the next pull.
I have some gouges in the ball, and was concerned about those at 1st. I let my local trailer shop look at it, and he said it was nothing to worry with, it happens. He had seen a lot worse.
The gouges apparently came from the coupler, and wondering if that happened when the guy that towed if from Elkhart had a worn ball, and he didn't use grease. Just speculating there. The gouges are not getting worse, so the coupler has probably smoothed out.
Chap , DW Joy, and Fur Baby Sango
2006 Ford F150 Super Cab 4x4
2008 Surveyor 263