Just found this and a very cool project I must say. For the past 13 years I've been in the mining business. In a coal mine I drove three different size Komatsus and in the current gold/copper mine,one of my first pieces of iron to run was a Cat 793F. Engines all yellow and no rust on the box. Dump boxes are repaired and rotated on an ongoing bases. The inside of the boxes are painted yellow but due to all the rock dumped into them they quickly go to bare metal. For realistic weathering you want something like this, very dusty, or if its raining, tons of shiny mud...

However, its your model and you do it as you as please. I have to say that I really like the rust effect

Hi Mark @markh, they are replacing all the main drains and water supply pipes where I live in China. I know it’s only a tipper and not a dump truck, but I thought you might find this picture interesting.

This truck turned out superbly, Mark @markh
Great headline article.