This thread is for anyone that has tips for any new user that wants to export their model from Google SketchUp to 3D Rad, whether it's from the warehouse or they made it. Here are mine from my experiences using it:

When you want a big city model in 3D Rad, it is best to have 2 separate files, one for the static rigidbody and another for the skinmesh. You can paint the entire model white in the rigidbody file because nobody will see it.  You can change the texture in the skinmesh file.
If the model has lots of backfaces (grey coloured faces), in the rigidbody file, press Ctrl-A and right click the model. Then left click on Reverse faces. You can see all the grey faces and you simply select the face, right click and click on reverse faces until the whole model has all while faces.

If you get the "Could not load rigidbody.x!" error, it means there is too many faces in the model and 3D Rad can't load it. You need to remove some faces or make the model smaller by removing sections of it.

Since exporting takes time, you can reduce it by selecting the whole model by pressing Ctrl-A, then right clicking the model and then left click Explode.