Thanks guys!
Chris: Yeah, everything was airbrushed. I've seen people here and elsewhere get spectacular results with pigments and pastels but I've never had much luck with them. Most everything here I borrowed from Steve Zaloga, I've tried a number of different styles but really like how he does stuff.
I just painted the thing in olive drab and then used the hairspray technique for the whitewash. You just spray some hairspray over the olive drab and then apply an uneven blotchy white coat over that. When it's dry take a moist (not wet!) stiff brush and drybrush it over the high points. The white will come off in an uneven streaked finish.
The 'mud' was just 'stucco' paint from the craft store applied over the lower hull and running gear in an uneven clumpy effect. Then I sprayed it all with Tamiya dark earth. I highlighted this with a little Tamiya buff working up the hull to blend the olive drab and white upper hull to the muddy lower hull.
On the Sherman I'm working on now I tried the hairspray technique on the 'mud' allowing me to chip and flake it away in places and get some nifty rain streaks on the mud splattered on the hull.