The basing tutorial is here: http://www.advancedtautactica.com/viewtopic.php?f=21&t=18333&p=229997
I use the same technique on all my bases to a lesser or greater degree.
My Chocochip Guard have the same base but it is then lightly drybrushed in bleached bone to make it look more sandy.
The paint chips/weathering was done like this....
Random blobs/slashes with black on positions likely to get scratched
inside the black blob add a splot of boltgun metal
wash with devlin mud.
The mud is done using a large dry brush and do not clean the brush just swap between the colours
1 Scortched brown and a "wet" drybrush method apply the paint to the lower hull, mudguards and tracks
2 Bestial brown normal drybrush over the scortched brown in patches and slightly above the border of the scortched brown
3 Graveyard earth and a dry drybrush over the previous browns and slightly above the border of the bestial brown.
4 Devlin mud in the armour joints and on the tracks where you have applied the brown.
you can also drybrush black around the exhausts (I normally do this before the mud).
do not apply too much brown - it is always easier to add more than to repaint the green