Jack

That looks amazing. Thanks for the tip.

Thanks to all

Another method for a dusty and slight build up of dirt on the lowers is to lay the model on it's side.  Sprinkle appropriate coloured weathering powders on hull, then on the edges add Tamiya acrylic thinner (the one that smells like rubbing alcohol) with a large brush.  

Once the entire hull side is soaked, return it to proper sitting position and let the excess drain downwards, causing natural streaks.  Repeat for the other sides.  Can also embelish further with downward brushstrokes both wet and dry.

regards,

Jack

As an alternate to pigments there is a 'stucco' type textured paint I like to brush on for mud and then paint. The results aren't as good but personally I find it easier to use. 

Thanks!

I think this gives me a good idea how to approach this area.

The paint should be a little darker on the lower hull than the paint on the upper hull, decking and turret.  They upper parts of the tank is exposed to the sun more.

That area on a tank gets pretty filthy. I like to use the earth tones like Sienna's or Umbers there, depending upon what look I'm trying to create, dry dust or wet mud.