Chromium plate is porous! Therefore it is important to try to prevent
dampness passing through it to attack the metal underneath. Good
plating has Nickel underneath as well, cheap plating doesn't have
enough. a good wax polish should help to seal the surface and always
liberally coat the rear of the bumpers etc with Waxoyl. Not so long
ago it was usual to paint a special coloured varnish over the chrome for the duration of the winter but,since modern cars don't have much
chrome it is probably not available any more.