This is a good reminder to all of us: check your lpg tank, lines and connections at least annually. If you see rust is increasing or started, do something about it. Use soapy water and a small brush to check for leaks on the connections. It just takes a few minutes to do a pretty thorough check on this stuff and certainly pays off in the long run.
By the way, Krylon makes a paint now that can be sprayed directly over light rust. I used it with excellent results on an iron gate a few years ago. It seemed to encapsulate the rust and I guess the paint kept oxygen from getting to it. Hasn't flaked off of the metal gate in all this time.