I've just completed this model and diorama in 1/18th scale. It is an old Mercedes SL that I have made to look like an old wreck that has been abandoned years ago and is ready for restoration,
I upholstered the seats and then aged them to look like cracked leather, there is also tears in the leather with the stuffing of the seat peeking out. I created the rust on the car using a variety of tools, materials and paints. I'll be doing some more shortly so I'll try to take some progress shots and post a step by step guide if any one is interested.