trailer/aluminum cleaner?

[Ikan Besar]

I have my (rather costly) aluminum boat trailer parked beside my house in Florida and due to the number of trees around, it's in shade nearly all day long. As a result of a humid climate, rain, etc. my otherwise perfect trailer (less than 50 total miles on it since new) is now green! I've asked around and can't seem to get any decent suggestions as to what product might help turn it back into the shiny silver trailer it once was not so long ago. I've tried soap and water until my arms are about to fall off. Any ideas for anyone that has been down this road before? thanks