Howdy Guys,
A member named Bernie over at
www.cardmodels.net offered a thread on his build of a wwII jeep. He weathered it as he went along by using milled coffee for mud, you can see the full thread here:
http://www.cardmodels.net/forum/show...highlight=jeep
the first post on the second page gives the recipe for the "mud". here is a photo from that thread, although this is a paper model, the effect should be the same on plastic:

here is a synopsis of the recipe:
coffee trick was done as follows:
- apply glue on model
- apply coffe "sand" on model
- brush softly with soft brush - to get away not glued parts
- apply chalk dust
- can be applied little bit acvarel colours where needed
Notice the "mud" behind the front tire:

Anyway, I thought this was such a good tip I would share the thread with ya'll. And I want to thank Bernie for posting this thread over at
www.cardmodels.net .
Have a good day all,
Greg aka GW