im not sure of the exact look u want, but a friend of mine tried somethin like that on a 63 chevy pu.he just prepped the body real good, but primed it with cheap rattlecan red primer( walmart specil stuff) then set it outside...after few weeks it ahd faded the primer an was lettin minor surface rust show thru..looked nice an grungy! soon as he got the look he wanted he wiped it down with metal conditioner an so far it hasnt rusted any further..just gotta kep an eye on it. The conditioner kinda blotched the primer but tat jus aded to the look! ight not be the style u want but it was a good cheap homebrew.however the style the other guys mentioned would probly be a lil safer an long term with no worries bout yer project suddenly rustin out from under ya!