I think I would model the bunkers in max and export .obj to import into TG. What you will have to do is somehow flatten the area they'll be positioned, which you'll have to do with an image map I would guess. Actually, it won't be easy with the road and steps built into the hill either, you may need to use World Machine or Geocontrol to help flatten out an exported .ter from TG. How close will you be getting to these objects? Will this be an over view of the battlefield, or are you expecting to green in some actors and use this as a virtual set?