My tip would be: Get a die-cast car in the right scale, hit it several times with a large hammer, stick it to a M.D.F. base with a hot glue gun, add rubble to taste, fill any large holes between car and base with putty, add sand and glue to taste, let stand (now is a good time to watch Mad Max or Resident Evil 3 or whatever...), spray black, paint to ability...Voila!
