To prevent the lug nuts on my trailer from rusting due to exposure to salt water, I cover them with rubber chair feet filled with grease. You can find replacement chair feet (the rubber cup on the bottom of a folding-chair leg that protects the floor) at any discount department store. I pack each chair foot with grease and stick them on over the lug nuts. They keep the salt water out of the threads, and the exposed parts packed in grease, and have done so on my trailer for seven years.
Robert Webster, Wesley Chapel, Florida