Rock salt is hygroscopic at something above 80% humidity. CaCl is hygroscopic above 20% humidity, making it 'sweat' in most North-American climes. Warmer temps speed corrosion, and freezing temps can ****** it, thought these are typically secondary to a chemical's innate corrosion potential.
Know what your demon really is. Here in MI we mis-credit highway 'rock' salt for the tremendous damage from CaCl dumped regularly on unpaved roads to keep dust down and cement fines to gravel. Depending on how far one lives 'off the pavement' many of us have more underside-washing to do in Summer than in winter.
Those who deny the basics may be doomed to trade in a rust-bucket. (eg: unwashed student commuter iron) That said, there is no substitute for prodigious rinsing whenever in doubt. If a tarp wouldn't flap too much and ruin paint, I'd want the extra coverage to minimize what 'spray' could seep into tiny spaces. btw, parking outside in the weather/rain for a day or two when warm, and/or plowing snow when it's coming down 'wet' are IMO underrated 'cleaning' shortcuts. (no cabs, please)
Agree that liberal dowsing of exposed metal with WD-40 is usually a good thing to do. Also know of a trucker who trigger-sprays Armor All under the hood of his own cars/trucks after a light rinse at a DIY car wash. (No rust, no dust, and 8 YO cars looking like new dealer demos.) btw, the 'cleanest rinse' can invite corrosion if we don't 'post-treat' bare metal to minimize flash rust. Just my $2.02.
