Lovely idea Red120, crazy crazy you.
I think what you should do is to first base them brown, then have drybrush of Bleached bone. Not to dry, this is such a time where that "a little to wet drybrush funginess" can be just what you are looking for. When this is done, make some fine lines close to the edges in a darker colour, maybe use a fine tipped pen instead of a brush. Then have a go with a little darker bleached bone, add a touch of brown, but in a rather thin layer.
Make sure to get an uneven coverage with the paints to show that this is not the first time them boxes seen battle...maybe add some bulletholes
I think what you should do is to first base them brown, then have drybrush of Bleached bone. Not to dry, this is such a time where that "a little to wet drybrush funginess" can be just what you are looking for. When this is done, make some fine lines close to the edges in a darker colour, maybe use a fine tipped pen instead of a brush. Then have a go with a little darker bleached bone, add a touch of brown, but in a rather thin layer.
Make sure to get an uneven coverage with the paints to show that this is not the first time them boxes seen battle...maybe add some bulletholes