After the basecoat dried, I started weathering the model by applying various shades of the base colors to give a very worn and used appearance to the models.
I continued the weathering process by stippling Andrea Color AC18 Reddish Brown to the models, followed by some Vallejo Model Color 177 Oily Steel. As the process went on, I added a little orange paint to the reddish brown and applied it to the already "rusted" areas. I then stippled some shades of green around the rusted areas to give a layered appearance.
I applied a dark wash to the models, and then went back and highlighted some of the areas that were too dark.