I cleaned the top completely and even filed off the sharp burrs that were still present from the original spot welds. Underneath I hand sanded as well as I could and epoxy primed, sealed and painted it. Originally it wouldn't have gotten fully sprayed as it was difficult to access (mine had lots of bare metal showing), but I wanted to clean it up better so it wouldn't flash rust again. It's mostly hidden unless you look up from under inside the trunk, but I wanted it as clean as I could get it. It's not perfect my any means, but it does look pretty good overall.
I bought new. I think a mild cleaner on a rag would be best to clean it. Nothing too harsh as it would possibly damage the coating. I would test it on a less conspicuous area first to confirm it doesn't damage anything.
