Fortunately battle damage is wide open so a lot of different techniques and skill levels can work well. The thining out of the styrene that these guys have mentioned is the most important in my opinion. Then you can do whatever you want with the plastic, puncture in for bullets and shrapnel or pull out for explosion. I like to heat the piece against the light bulb in my work lamp, it's usually right above my head and it's slower so I have more control. The fenders here have been bent that way and the small pitting and damage to the front plate are done with a dremel by bouncing it.
There will be plenty more hurt put on this Tiger, I just included this pic to illustrate how the subtle can also work as 'damage'. Have fun with it, who's to say what metal will do under the punishment, if you go too far, then it's really, really damaged, right?