Install | Import | Export - A vehicle in Zmodeler 3 and then on the game (video ENGLISH | FRENCH)
There is a complete tutorial to learn how to install a car correctly on OpenIV to get it works on the game
AND how to import and export a vehicle on Zmodeler 3.
This is a video tutorial, voice in french BUT english subtitles availables and english description too ! (thanks to Rappo for the help, you can help by translate in others languages if you want )