I did these a while ago, using the vallejo airbrush rust and chipping technique. I'm pleased with how they turned out even If I need some more practice. It does give me the look I want though and works really well with the ruined buildings from Mantic Games.

Also shown here are some Imperial Trenchers from Warzone: Resurrection. just to give some more life into the pictures (I try this some now and then). More terrain stuff soon!