Thanks guys!
Mike: Lol, I sprayed the base with matte varnish but it still looks shiny. I decided I liked the shiny 'wet' look so I just left it that way.
The base was a cobblestone rolling pin from Green Stuff World in Spain. You just cover the base in plaster and then roll the pin over it granting a cobblestone finish.
http://www.greenstuffworld.com/en/amazing-tools/562-mega-rolling-pin-hobby-roller-cobblestone.html
The plaster had some dips in it that didn't cover completly so I added some leaves over the bad areas. Here also I used a Green Stuff World product - a leaf punch. You just stick a leaf, coloured paper, or whatever in there and punch out a miniature 'leaf'.
http://www.greenstuffworld.com/en/101-punches
Captain: Thanks! This was a post-war tank though. The French didn't start production until 1944 when the Germans were run out of France. I like the idea of a cow, and I have Tamiya's livestock set- I may have to stick a cow in a future build...