I do the rust perforation with a very fine Dremel tool, as far as the rust itself I soak triple zero steel wall in water until it turns to rust, run it through a screen, and apply it over a satin lacquer clear then Dust the whole thing with hairspray when you're done
That is cool. You have that Midwest rust down pat. I used to do junkyard models years back, but they were merely missing a front clip or a motor.