Metal covered trunks in a nutshell.
If you have a metal covered trunk in good condition the best treatment is minimal treatment. You can apply oils or wax but generally this will just attract dirt and dust. Additionally, wax needs maintenance, ie. buffing, reapplying, occasional stripping, and then reapplying. An endless cycle. Just wash it with a very mild soap solution and then dry it. It leaves a nice, subdued patina.