Argentine grills are not coated. If you want to keep them from rusting, you just grease them a bit with the remains of the meat (you usually don't even need to do that) and clean them up next time around. If you are really concerned about the rust, you can always coat the grill with vegetable oil (just take a paper napkin, soak it in vegetable oil and lightly rub the grill with it.)

BTW, the biggest unrelated tip: when you are seasoning meat, use kosher salt instead of fine salt. It works much better!