Issue with exploding stages

[TiktaalikDreaming]

(Note: Title edited to sensationalize the issue)

I'm working on a mod to recreate the Convair Nexus (http://forum.kerbalspaceprogram.com/threads/121017-WIP-Convair-NEXUS-super-heavy-Earth-Launch-Vehicle). Many of the second stages use twin rocket engines, and these would be covered with a conical decoupler. The basic layout being a fuel tank above, then 2+ rockets which have either their own stack nodes or are (as mine currently are) surface attached. The decoupler (which is a big cone with a series of colliders to form a hollow) is attached to the tank's bottom stack node. Then the next stage is attached below that. The theory being, when the stage is disconnected, the engines slide out from the hollow of the decoupler's collision mesh, and off you go. And here's what should happen;

The problem is, the engines keep hitting the edges and I've made them a bit explosive (this stage engine was to be gas core nuclear, which is a bit reactive), and so the result is usually one engine clips, explodes, takes out any other engines, which also explode, and I have a full tank of juice with no rockets, spinning madly in orbit.

Thusly;

The question is, have people run into this before? And, if so, what do people usually do? I know I've used this system with parts from the FASA mod without encountering the same issue, but the mu file import doesn't tell me a lot about how collision meshes are configured, so I can't figure out how they solved it.

Any help is appreciated. :-)

[TiktaalikDreaming]

Never mind. While doing my best to explain the issue, I pointed myself at the solution. Make the collision mesh a single non-convex collider, and it all seems to work.

Carry on.

[raidernick]

For future reference, all decoupler colliders should be non-convex and hollow. Convex colliders are fine for intersecting meshes when they are attached permanently, but for anything that is going to detach they can't be touching or intersecting at all.