Unity gives me
1: Quaternion inertiaTensorRotation : The rotation of the inertia tensor.
2:Vector3 inertiaTensor : The diagonal inertia tensor of mass relative to the center of mass.
I assume that I should rotate the inertiaTensor by the inertiaTensorRotation.
Using a matrix may work if its true that.
Matrix4x4 m = Matrix4x4.TRS(rigidbody.centerofmass, rigidbody.inertiaTensorRotation, rigidbody.inertiaTensor);
I guess I will need to test this out.