Actually I think I can merge them in blender after UV mapping. But I am not sure if this has any unwanted side-effects.
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Thanks
:
Please notice the vertex-count. It has doubled because I exported it form blender with ‘Flat shading’. Otherwise the model wont look nice. It will average the normals at each shared vertex and this results in a mesh that is too smooth.
Another problem. There is gap on the floor at the very back (near the pillar, behind the hut). Also there are plenty of hidden polygons and there, and some faces (especially the hut) has double faced polygons. I have not UV mapped those faces, so if the camera cuts into the mesh, the result is not very pretty 
@everyone else:
The model contains a hidden pillar inside the big tower geometry. I did not UV map it as it is never visible. If anyone thinks I should UV map it, please let me know.