I work in the marine industry, and the marine electronics industry specifically (radar, sonar, etc). You don't want salt water near anything. We do 28 day salt spray test on our products, and I can tell you, after a few days in a 5% salt solution at 35 deg C, steel will be significantly corroded. So will uncoated aluminum, so will most adhesives, so will most any plating you can put on steel. There are some coatings that work, but they are the ultra high end military grade coatings that cost $1000's per gallon. Run an electrical current through that metal while it's in salt spray, and the corrosion time is decreased drastically. An electrical current through gold plated, stainless steel, battery contacts will corrode the contact away to practically nothing, in less than a couple days.
I'd just use water and some biodegradeable antifreeze. The antifreeze will help minimize corrosion on the steel, for a small price premium. Figure a couple gallons of antifreeze is alot less than a new pair of rims.