That's a really nice model you've got going there, v.impressive

I'm not really a rigger by heart so can't really offer to much advice, but one suggestion would be to skin the organic and hard body surfaces seperately. Firstly smooth skinning the organic body parts and then skinning the hard body surface using rigid bind and fiddling with the membership of the vertices to all the joints to bend.

Hope this helps in anyway. And if anyone has a better suggestion, please feel free to tell me that i'm wrong.