i always use mop and glo that you would use to put on the fllor to mop with its works great

Use CLR in a spray bottle, don't let it drip on your trailer. Do one section at a time, wipe and rinse. Apply wax or Rejex when done.

Alumabrite will take off just about anything even rust stains put it in a bug sprayer and spray the boat let it sit a few mins then just hose it off don't do it over your grass it will kill it I would also put some wax on the boat after it's clean so it won't turn yellow

Try a magic eraser, they work pretty well, but if nothing else works alumabrite or something like that will definately get it off but make sure you wax it after.