Don't fall into the rust trap when you weather. I've seen guys apply so much rust their tank looks like it sat in a field for 50 years and that's not the way these tanks looked in real life. These machines were very well-maintained and if a commander saw rust like that on a tank under his command somebody would get their ass chewed. In the end, it's your tank and you can do it anyway you want, but if you're going for historical accuracy, keep the rust to a minimum.