Mike, The weathering technics that have been given will knock the new shine off of rolling stock. If you want to weather rolling stock even more realistically, you need to look at color photos of the prototype to see how things weather. I was in a rail seminar at work a couple of years ago that emphasised various aspects of working on intermodal trailers and refrigerated railcars. One part of the seminar was safety and blue flag laws. The instructor for that part of the course was the supervisor of the car shops for the BNSF in Yakima, Wash. Someone asked a question about cleaning freight cars. His response was, "Freight cars are to make money. We don't wash them on the outside, or paint them except as required for maintainance. We don't care how they look as long as they do the job safely." The railroads do clean the inside of cars between loads if needed, but not the outside. The only cleaning the cars will get is when they go through a rainstorm. Also think about the use of the cars. Boxcars carry all sorts of comodities. They will tend to rust around rivets and doors. Plug doors on a boxcar or reefer weigh 1500lbs each. The tracks will be kept greased to let them open and close easily. That means that you would want to paint a little black on the inside edges of the door guides. Still, some may need to be pushed open or closed with a fork lift on occasion which will scratch the paint and start a rust spot on the bottom of the doors at each end. I have a few small hoppers in my collection which are painted for Santa Fe and used in cement service. I went to a craft store and bought a bottle of water based acrylic craft paint that looked like a cement color. These hoppers carry powdered cement in bulk, not bags. They are loaded from above out of silos, so I expect that some of the cement will spill next to the hatch, then rain will wash it down the side of the car. I thinned the paint with denatured alcohol to a thin wash and applied it to the top of the cars with a brush letting it run down the sides. Open hoppers are not loaded gently. Whether they carry ore, or coal, whatever will be dropped in by some sort of loader. There will be no sign of paint left inside except maybe at the very top of the inside. They will probably not be rusted inside except for a very light patina when empty. The inside of an open hopper will be bare steel from loads constantly cleaning off rust and paint. Everytime coal is loaded into a hopper, it is just like sand blasting the inside of the hopper. Gondolas will tend to be the same way, but not always. If the gondola is used to haul scrap metal, it is just dumped in and will make the inside look like a hopper, but if machinery is hauled in the gon, it will be loaded carefully and lashed into place to protect it. When the shop I work at was located in downtown Los Angeles, there was a company right behind us that manufactured tanks. They would receive gondolas loaded with steel in various shapes and sizes. There would be plates, rolls, and angle iron of various web sizes. The steel would be stacked carefully, banded, and loaded on wooden blocks to protect the new steel. As soon as the steel was off loaded from the gons, the empty gons would stay on the tracks and become scrap metal bins from the tank manufacturing process. When the gons were full of scrap metal, the railroad would pick them up, and deliver a fresh load of steel. The new steel was stacked carefully in the gon, but the scrap was just thrown in. I hope this will give you an idea of how to weather different cars.