Although this post might be a bit old (and already resolved), I would like to add my two cents when it comes to animating vehicle sliding doors:
Before importing an LRV sketchup model into V3DM, assign each inside face of the door a different material. The outside face can remain their true colours. For some reason in V3DM, all faces with the same inside and outside faces of an imported sketchup model can only be selected simultaneously, not individually. After importing to V3DM, group the faces that belong to each door. Now you can define these groups as doors in V3DM. Vissim will automatically determine the sliding direction for each door.