The dio looks great so far Larry but I'm curious when you say you will be adding "real mud and snow". Is that literally what you are going to do or slip of the tongue? I reckon if you covered the foam with some sort of artificial mud and snow it would look superb. When I created my winter dio, I just covered the foam with plaster and paris, let it dry and then painted the road areas in an earth colour and then sprinkled artificial snow on the rest. I'm sure there's better ways than mine in getting a nice affect though.
Tom