Ok, here's what I can tell you. I did use Bullet physics for the rigid body demo which you can download here:
http://www.thermite3d.org/releases/ThermitePhysicsDemo.zipHowever, I don't have a source archive corresponding to that release, and I don't use Bullet in Thermite any more (but it will probably come back in the future). But according to
this post I released the demo in April 2008, so if you get the SVN version corresponding to that date then you should find the Bullet code in there.
It's probably too hard to try and build it, but you may be able to look in the code to see what I was doing. As I recall I made use of a standard Bullet mesh (maybe this was the btBvhTriangleMeshShape?). Actually I had a number of these corresponding to different parts of the volume, so that when the volume changed I didn't have to update the whole thing.
I recall that a limitation was that I couldn't have interaction between two concave objects, so the rigid bodies had to be convex. It's also worth noting that I was using the OgreBullet wrapper for this, though next time I'd probably just implement it myself.
As for the crash I can't help you, you'll need to look in the debugger.