Salt-Away is also what my brothers and I used back in PA to combat the winter salt, and which I continue to use here in Hawaii.
Ideally, drive to the self-serve car wash, pressure wash the underside to knock off the big stuff, spray on Salt-Away in a garden pump sprayer with wand, and rinse off. Or do it in your driveway with your garden hose and wand extension.
What's nice with the Salt-Away is that it's non-toxic, water-based, solvent-free, biodegradeable, and safe on everything I care about (metal, paint, plastic, chrome, rubber, wax). It's also good for boats, PWCs, scuba/snorkeling gear, marine aquarium equipment, et cetera.