Mesh Collider falling through?

Here is my model. http://img17.imageshack.us/img17/8126/cubemodel.png

I have also made some small cans, a pipes, a custom crate and a wheel in 3dsmax. This is the garbage items that I want to lay on the floor.

In Unity, I have applied a Mesh Collider on the big model. Then I put the small item models in the scene and drag them inside the model, "hovering" a few inches over the floor. Then I also apply mesh collider on them and checkbox "convex" on all of them. And the ridgidbody after that also ofcourse.

When I run my game, my crate and my wheel gets stuck on the floor, rest of them falls through the ground. What have I done wrong?

Do I need to apply mesh/rigidbody in a specifik order or something?

Ask me if I explain bad.

Thank you!

Have you checked that the "Trigger" checkbox is not set?

Also, the mesh collider of the interior model should not be set to convex.

And when the objects are very small or move very fast, they might drop through other colliders.