Any even slighly exposed metal will be rusty. This wil also leave rust streaks down the side where water would flow from the metal. Rivets are likely to develop rust streaks. The tracks will be very rusty. Any metal on the wheels that were once polished by contact with the tracks will be rusty. Edges of open hatches will be rusty. Exhausts, naturally. Any tools left on the vehicle will corrode. The inside of the barrel will be rusty and likely the tip as well. If it's been out there a really long time, the rust will spead away from the exposed metal and make the paint bubble. As this breaks away from the surface of the vehicle, you will have larger areas of rust. Thin metal, such as head lights and horns and the exhaust will develop holes, too, from the oxydation.
Remember what Neil Young said, "Rust never sleeps!"