Did some quick modelling with GF9 green stuff the other night to add some extra detail to my FOW Fallschirmjager infantry by adding sandbags to the Mortar Platoon, one of the HMG bases in a combat platoon, and eventually around the Pak40s in the AT Platoon.
One mistake I did make though was applying the additional static grass to the bases BEFORE the greenstuff had dried and hardened, hence the various pieces of static grass stuck to the various sandbags. Painting wise I think they will need a basecoat of Chaos Black then alternate layers of Scorched Brown, Deneb Stone, Bleached Bone and Mud Wash to get them to the right colour.
Also considering options for creating camo netting over the top of the Pak40's by putting sticks into the corner of each base around the sandbag walls and putting some kind of netting equivalent over the top - like the picture above. Maybe a hairnet or pair of old stockings with flock stuck on it?