Not sure I can answer your specific question, but I am afraid the only cure is to replace with plastic. I had galvanized wheel wells on an SOB. It was delivered to the dealer in February 1993 in Michigan....(spelled salted roads). Within two years, ti began rusting badly. Tried all the tricks in the book. At about 4 years of age, I bit the bullet and replaced with the plastic ones they had started using in Manufacturing. They provided the wells to me for free, which was kind, but it was a job installing them. I suppose you could have some fabricated out of stainless.......
"If the women don't find you handsome, they should at least find you handy." - Red Green