Thanks Jesper!
I used windsor soft white mixed with bio-safe oil thinner (odorless and non-flammable). Now, the ratio was personal preference but I started light, so that the base color and weathering would show through. I applied probably three or four of these washes before I was satisfied and then added a light wash of windsor raw umber just for starters. After this had dried, I began "weathering" the whitewash randomely as follows: spot washes of the base whitewash in various areas so that a stark white was present against the raw umber dirty white. This gave a nice contrast. Next, were spotwashes of thinned tamiya clear coat on the edges and bolts. Then, raw umber, burnt sienna and black pastels were "dotted" in places I chose and then dulled down and sealed with thinner. I used grumbacher raw sienna thinned down on the tracks with a dry-brushing of tamiya clear thinned down. At this point, I started adding MMP earth and medium earth and spread this around with thinner. Again, how thick and the location is personal preference and what is satifactory to your "eye". In addition, many light washes of MMP earth dirt over the front and rear followed by very light dry-brushing of the base dark green color (tamiya) on the armor plate edges. I did a lot of experimenting - also, what look like chips of paint on the front top hull are dots of pastels, MMP powders and small dots of raw umber oil sealed by washes - lots of them. You just keep going with washes until the surface texture is to your liking.
Charlie