Here is another tip for model makers: NEVER allow your export plugin to do the Mesh Converting for your object. This is what leads to most problems that people encounter. In your modeling program you should be sure to convert each part manually to a MESH (editable mesh) - that way you can control the normals, and polygon distribution to suit the needs of your object rather than have a converter use some SINGLE conversion factor for the entire mesh. Then when you export be SURE that only the MESH objects you created are selected otherwise the converter will merge your mesh with any other surfaces that it has converted - duplicating everything and resulting in a BIG MESS.