With covered hoppers I generally decide first what is going to be hauled in them. They are loaded from the top, so whatever thay are loaded with will tend to spill over the sides a bit. To dull the plastic shine, I use dull coat. For water base paints there is Floquil Polyscale flat finish. The flat finish can be added before or after the weathering is completed. Some loads like concrete, will tend to spill over the top of the hopper and be streaked down the sides, other loads, like plastic pellets won't stick at all. Dirt will tend to be kicked up in two streaks by the car in front and back of each car in a train. A little dirt will tend to accumulate along the bottom of the car on each side. Dirt and dust may also fall on top of the car when sitting, and then when it gets rained on it will tend to wash down in streaks, usually kind of subtle. The dirt will change color depending on where it comes from. Clay found in Georgia will tend toward a red color, but probably a bit more brownish than the red dirt you will find in the Southwest through New Mexico, Arizona, Utah, and Southern Nevada. Rust will tend to start at rivets, or at any point where the paint is damaged, and the rust stains will run down from the source of the rust. Finally, you will get smoke and soot all over the car if it goes through tunnels more so in the steam era, but in diesels as well.
