vehicles currently need setup inside Skyline and not the modelling package as it currently cant be done.
In your modelling package, take the car body and export that as a mesh and take the wheels and export them as a mesh.
(by mesh i mean the format you use for exporting e.g. .obj, .dae, etc...
)
Then use the .car file or the lua script to set your vehicle up.
There are 2 tech demos with the new version of skyline.
One for .car and one for lua script.
For .car vehicle setup, use the examples in the models/vehicles folder of the asset library and this wiki page
http://www.chi-ad.com/DokuWiki/doku.php/res_vehiclesetupHope this helps