I reworked the Opel using the Lifecolor rust set. The colors are very good to use, they can be thinned very heavily and still dry totally matt. Here they are:
I applied these (from light to dark) on the already rusted areas. Then I applied pigments in light colors (light dust, concrete etc).
The look of the debris was enhanced using different pigments (brick colors mixed from pastel chalks, rubble) that I sprinkled over the bricks and then fixed using pigment fixer.
As a final touch I also added some dark oils to the rims of the steel door.
This is the final look of the diorama base:
To achieve a better fit of the figures to the base, I applied dirt using different oils and humbrol colors. Humbrols were used for earth colors, and oils for dust and traces of brick dust:
Now the figures are ready to be fixed to the base. Then I will finish the helmets and the weapons.