I've been ignoring this project for a long time because I didn't want to start weathering the road wheels and tracks. I had plenty of time to concentrate on this today so here is another update:

Tunisian Tiger I (My Father's Tank)
The tracks came molded in an appropriate rusty color. On the inside of the tracks, where the tires "polished" them, I sprayed a light coat of Metalizer Exhaust shade. On the outside I gave the links a dirty wash with very thin black. After that dried it was time to hand brush a coat of Metalizer Magnesium to the tread bars. After the magnesium dried I used some silver/grey powder to highlight the bars a bit more. Tomorrow I'll experiment with another light wash on the outer face of the tracks.
The sprockets and tension wheels were silvered on the teeth and rims with a silver Prismacolor pencil, then this was rubbed to remove some of the material.
The next step will be with pastels to accumulate some grime, but I believe this will wait until the tracks and wheels are assembled on the hull.