There are programs that allow for CSG (constructive solid geometry) where you can do that Moray/POV Ray or Spazz3D are examples.
The DoGA CGA series is based on a parts metaphor. Easy to use, but you have to build custom parts by creating them from small bits. The latest Version (L3) allow for the importing of DXF files so you could build a damaged part externally and bring it. You can get clever with certain textures and create transparent sections and then build an interior. This is a lot easier with L3 since you can build a damaged section or create a transparency mask to mimic battle damage.
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TAZ
As an example...
http://zircher.iwarp.com/fots_3d/contest03/drifter.htm