[arttorney]

After a very little testing, I have confirmed that SketchUp 7 free version (which readily exports as Collada .dae files) can very readily be imported to Meshlab (a FOSS mesh editor) which will then very readily export a triangle mesh of your model as an .obj file.

Meshlab apparently also has powerful tools to clean up the mesh, merge meshes, and close the holes etc. so you may as well clean the SketchUp file before taking the file over to the next tool.