After looking a many photos I had an afternoon of van weathering. The consensus is that most post 70s air-braked vans are paint-faded and dusty. the fade is a tricky one putting faded paint on as a base colour is one thing, but fading paint that is already there? I just went with the brake dust and grime. No German grey this time which is unusual for me, just a bit of brick red and earth (Humbrol acrylics).