I would first try washing the black marks gently with auto shampoo, water and a soft sponge or rag, as if you're just washing your Airstream. Don't rub too hard; you don't want to damage the underlying finish on the aluminum.
If the black marks don't come off by just washing the panels, I'd try a little auto wax (like Turtle Wax or whatever you have handy) in a small area, to see if the solvents in the wax will loosen up the black stuff. It might just dissolve and rub off. If that works, just wax the areas where the black residue is.
Next, you might try an art gum eraser. These are made of soft gum with absolutely no abrasives that will cause scratches. Again, tray a small area first.
Do not use anything abrasive, like Bon Ami or Bar Keeper's Friend, because this will damage the finish and scratch the aluminum. Basically, don't put anything on the aluminum panels that you wouldn't put on the painted finish on a new car.
If none of the above works, you might try a commercial "goo" remover, like Goo Gone or a similar product. Just try a small area to see what happens before smearing it all over the side of your Airstream. Be careful, as some products contain strong solvents that will dissolve clear coat and whatever other finish may be applied to the aluminum panels.