If you take cork roadbed and triple it up side by side, it is the exact same width as a wheelset. So you snug the wheelsets down onto the cork strips to hold them still. I took a 10 inch section of roadbed, tripled it up...stuck a few long nails through it to hold it together (which made a great stand of sorts) and placed about 20 wheels on it and shot it with Polyscale "rust". Turned it around and shot the other side
It took me the longest time to figure out how I was going to hold those wheelsets still while I painted them. Now I know. Hope it helps someone.