If I understood correctly you want to simulate cloth on a model that has thickness?
You can do that with PhysicsMesh. It’s basically just another model (usually a plane) inside, that is roughly of the same shape as your original mesh (or GraphicsMesh). You need to create your cloth simulation on that plane but apply cloth to your original mesh. This way your GraphicsMesh will follow the simulation on your PhysicsMesh. You can then disable material on the PhysicsMesh, to get it out of the view.
hope this helps~ 