Got to agree with Benihana - altho you've got the colours right (mostly), rust is more organic in the way that it forms.
Firstly, it pools and flows in the directions that the water will flow off and down the surfaces. Imagine the truck (in this case) is standing in the rain; where would the rainwater collect? That's where the rust will start.
Now, when the truck moves where will the water go to drain off? That's where the rust will move too, forming more rust, and rust coloured dribbles and staining. (Look at the rivets on the side of old ships.)
Also, when the rust dries it will make a tide mark around the staining.
Rust grows upward very slowly, lifting the paint and making it crumbly. But it also flows downward in a 'V' shape, and spreads sideways as it does so.
If you can, go to an old shipyard, or a car breakers and look at the rust as it is growing - it's almost like a fungus.