If you decide to undercoat an assembled vehicle, do a thorough steam cleaning or pressure wash first. Otherwise, the salt, road grime and other corrosive stuff gets trapped under a protective layer of tar so it can really do its job of eating the vehicle.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!