Here you go ---
FSM May 03 pages 70 - 73 "Mudying an armored vehicle" by Ron Poniatowski
Ron has collected actual dirt samples from various location across the US. This helps him mix acrylic paint in the desired shades. He mixes it a bit lighter than the actual dirt to keep size/scale/color ratio correct.
Making mud the Ron way - find a base dirt color, mix paint to match (mixing dark into light in small amounts), make the mixture - white glue + baking flour + enough paint to give desired color (glue is the binder, flour gives thickness), apply to AFV with toothpick (watch for a bit of shrinkage), use a toothbrush to spatter the hull. If its really thick mud use some actual dirt.
Making mud fly ---
1. Armatures - thin wire shapped as desired for the mud sling. Apply the mud mix right to it and let it dry.
2. Clear styrene sheets - cut a sheet as desired and apply the mud to the trailing edge as desired. You can layer these to add depth.
3. Waxed paper - sculpt mud on top of a sheet of wax paper (bend the paper as you desire first). Let it dry then peel the paper off the bottom. I bet this would work with aluminum foil too.
Once your method is dry then apply it by 1. drilling ahole in the dio base and inserting the wire. 2. etching a groove for the styrene or 3. gluing the mod where you want.
Remember to make the mud part of the base not just attached to the base. Work the mud mix at the base of the attachment point.
Check out the pictures they are the meat and potatoes of this article.
Check the last three images, mud, mud 2, and mud 3. Mud is the first one Mud 2 is applying styrene and three is the actual deal in action.
http://groups.msn.com/armorama/sloddersstuff.msnw?Page=Last