Can you convert the sketchup mesh into Blender. Then put the texture on if you have it seperate.
But can't help really as no idea about sketchup and how it works and only use the Blender Game Engine for my maritime routes and I don't need to bake on the textures. Barry
There are other tutorials available, see the Trainz index on that site.
Making Trainz models in Sketchup is only suitable for very simple assets; due to the way Sketchup creates meshes they can be very high in polygon count and use multiple textures which result in very poor performing assets when imported into the game.