I have created a model of a crashed trailor in maya. I put it on a cube platform with mesh colliders and a rigid body. When I put it onto a terrain, it sinks through. Is there a solution?
checkmark the is convex box in the mesh collider
mark as answered and have a nice day 
Remove rigidbody from your cube platform.
It could be that you need to move the model higher up, as it may be starting just under the platform. Also make sure that the platform does not have trigger checked in Mesh Collider.