Are you doing this because your game is crashing or you're preparing a mod pack or you have free time?
I think there are mods and tutorials to help you do this.
However if you want to learn how to do it yourself, like a real boss, then download a vehicles pack, open it in OpenIV, look at the simple structure and examine the meta files. Very simple.
Two drawbacks.It's a PITA Good luck troubleshooting 20 cars in 1 dlc if you make the slightest mistake.
Or text tutorial