I know there was a thread about acid washing recently but did not notice if anyone said anything about the best wasy to clean up a steel trailer.

Can you acid wash steel? Will it harm my awning? What about the truck - should I unhook the trailer to wash it?

RIDE ON!

I wouldn't bother to acid was a steel trailer. The whole point of acid washes is to get a chemical reaction with the aluminum effectively eating a thin layer of skin away leaving shiney new metal. You don't get the same chemical reaction with steel. It generally won't harm painted surfaces but it won't clean it either.  I would scrub it down with diluted "Simple Green" then apply car wax. If it's not too far gone it'll look nice.

Good luck, PTA