Abrasive pre-cleaning such as SOS pad, green scrubber or bar keepers friend is a good idea. Polish is just that a polish some will have a measure of ability to remove oxidation but if it is heavy oxidation you essentially want to "smooth" out the metal first with abrasive that is appropriate to amount of pitting then polish.
In my case I did a bit of steel wool but you MUST make sure to get every bit of the steel fibers rinsed off (steel and aluminum corrode each other) Followed by bar keepers friend and some of those green scrub pads. Used some Nevr-Dull (link at end) tarnish remover. Finished off with this product. Simichrome leaves a film behind that helps protect and provides a brilliant shine.
Amazon.com: Simichrome Metal Polish: Automotive
Simichrome can be found at some auto parts stores as can NevR-Dull but I think I got the NevR-Dull at Ace Hardware.
I did run blue masking tape along the trailer surface next to the aluminum to prevent black polish residue getting on fiberglass. I removed tape as soon as I finished each section. I have an old somewhat porous FG surface and getting the black out of it was a PITA.
Nevr-Dull link http://www.amazon.com/Basch-N-D-Neve.../dp/B0014IGAWO