I added some more damage and painted up the crashed Valkyrie's exterior today. I took the lazy route and used spray paint for the black undercoat as well as the green base coat. I did end up using a brush to apply some boltgun metal to the inside of the model as well as the heavy bolter.
I started the base of the terrain piece by carving up some foam rocks, putting them on a piece of wood and adding sand. I gave it a liberal coat of glue/water mix so I could spray it and 8 hours later (took forever to dry) sprayed it black. It's a bit hard to tell from the photo, but its about 12 inches by 12 inches.