I love painting rust, its really qucik and easy too.
1. Paint the model brown.
2. Spray on GW macharius solar orange with a tooth brush. AN old one mind, or the wife's
3. Wash with watered down black/grown mix.
4. Light drybrush with silver.
The peeling paint is then done as follows
1. Prime with flesh or bone colour, then apply the yellow.
2. When dry, run under a hot water tap and attack the paint work with a tooth brush.
Then after that its just a matter of finishing up. Cover any scratches where the base resin shows through, then do some dribbles in brown and orange. Jobs a good'un! I actually did a model similar to this in 20 minuets once. I used a fan heater to speed up the drying.