When adding a Trigger to a game object, and setting the Trigger Shape to Custom Collider, the check boxes for Trigger on Enter, on Exit, and on Stay disappear.

Any reason for this?

Also, any way for parent game objects to inherit the mesh colliders of its child prop objects? That way, if I select custom collider on the parent like in the above situation, I won't need to needlessly recreate a complicated mesh collider.