To get a SketchUp model, baked with Lightup, into Unity3D, you can use the integrated FBX exporter. This also works in the free version of SketchUp, which does not support FBX.
The integrated FBX exporter includes the baked lightmap and the secondary UV coordinates that are required in Unity, to have the two textures correctly mapped.
You should also install the Lightup support scripts in an "Editor" folder that you can create in your assets folder of your Unity project, as this will automatically assign the Lightmap shaders and load the lightmap textures.
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