Drybrush the pipes and cables with dark brown.  Drybrush the drain pipe, container and clothespins dark brown also.   
 
 
 
 

Drybrush everything on the barrel except for the couplers and tank wheels dark brown.
 
 
 

Drybrush the mantle and small tank wheels dark brown, along with the buttresses and the power cable below the barrel.
 
 

Now for the base color (I chose blue, but other colors could be used).  Drybrush the turret dome and base dark blue.
 
 

Drybrush the sides of the VHS case, electrical box, and building panels dark blue.
 
 

Now mix some light grey into the blue to make a blue-grey midtone.  Drybrush this over all the blue areas.
 
 
 

Finally, drybrush light grey highlights over all the blue areas.
 
 
 
 
 

Drybrush the couplers and tank wheels on the barrel with light grey.
 
 
 

Drybrush the blue areas on the turret with a light grey highlight.
 
 
 

Drybrush the top surfaces of the platform with light grey.
 
 

Gently drybrush steel over everything, taking care to highlight the finer details such as rivets.
 
 
 
 

Mix up a rust colored wash and apply it in downward streaks from any edges, holes, and points of contact that look good.
 
 
 
 

Rust washes can also be used along any joins and around rivets to add some depth.
 
 
 
 

Add decals / transfers as you see fit.  I use alligator clips to hold the backing paper in position and push the decal onto the model with a wet brush.
 
 
 

Once the decals have completely dried, flat coat them with some flat laquer or flat coat.  You can dirty them down by mixing a little bit of dark brown into the flat coat.