To fill rust pits, and especially the pinholes, the body shop I once managed used Devcon Epoxy Steel. I think the name has changed since then, but the product Devcon sells these days is essentially the same. It's basically atomized steel powder in an epoxy carrier that's MUCH more durable than J-B Weld.
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!