Snow and Mud

I use eiter baking soda or bleached flour to represent snow.
What I usually do for mud, I actually make mud. Fine earth mixed with water and white glue is what I use to create groundwork. sprinkle snow material into ground, then immediately press the kit into the groudwork. The wet mud underneath will soak through the flour creating a very pleasing effect..

Awasoda,
I am trying baking soda for snow although am not done yet so I cannot say what the finished result will be. Just some white glue thinned with water and brush it on. Then, maybe a clear coat of some kind on the snow (careful though because what you use could discolor baking soda or make it bubble) As far as mud I would use a soft pliable clay for the ground so you can imprint the tracks in it and then just some black and grey paint. You can also find some small stones or hobby rocks and stick into clay in random spots. Then to give it a sloppy look splatter some onto tank and use some high gloss clearcoat to make it look wet. Just a suggestion though. Hope it helps.