Lookin for some good trailer soap

Soak it down with some Simple Green, then scrub and rinse.

 

If you have an industrial chemical/janitorial supply get some aluminum brightener.
Mix with water, spray down with a garden sprayer, blast off with a pressure washer. Sneak up on the concentration, "too hot" will sometimes turn the aluminum a white'ish color. Keep in mind, any wind and this stuff will carry and get on something you don't want it to. This is how I've done my aluminum trailers for years.
Blue Beacon used to offer brightener but I found the results less than stellar = waste of money.

 

I use a product from M P E washers in Lebanon In. called Panel Brite. Works good on the painted aluminum as well as the bare. Will take off the bird crap.

 

I use crud cutter. Biodegradable and works well. Buy it Lowes. I gallon is about 10 to 12 dollars. Let it sit 10 mins. Rinse it off. Works great on the black streaks off the gutters of my camper too.