Rain on the way home won't do it all -- witness a couple of years ago when, in
JULY, I removed the left rear turn signal housing on the pickup to replace a bulb - and found a big ol' hunk of salt - maybe grapefruit-sized -- nestled down inside the fender.
A winter of rain and snow and slop and all that -- still didn't get rid of the salt from Bville. I still think my idea would work best -- find a fast-running stream that's a little deeper than your vehicle's roofline, then park the vehicle in the stream for a couple of days.
That'd get most of the salt out.