As you will recall, VBuilder3D includes a specialized export module for Microsoft Train Simulator (static objects) and can create 3DS objects that can be re-exported to Trainz via Gmax.
More details on my site:
VBuilder3D, the 3D modelling product which I have developped and which enables the user to create 3D objects by a simple drag-and-drop juxtaposition of basic shapes, no longer has a demo version. The standard version is freeware, without any limitations in time, but users are limited to a maximum of 100 basic shapes per object. The "full" version needs buying a licence, and has no limitations of any kind.