I think the best thing that you can do is to either give loads an extra rinse or rinse out the machine after doing laundry, maybe with some white vinegar in the water followed by clear water to neutralize the alkalinity of what's left behind as that is the principal actor in the corrosion. If the metal dries in a more or less neutral environment, the pot metal's corrosion will be slowed. Any coating you could apply might have the propensity to trap moisture against the metal hastening the deterioration of the metal.
