you know.... you could just import a existing car with it's skl.. evne with dummies...
make own bones with names of these dummies and just rig a car
i mean thats not a huge problem or anytthing, if i remember corectly you need like... 5 bones minium for a working car
4 for each wheel and 1 for a main bone which is also a "target" which you aim to enter a car
additional bones were for like more seats, lights etc... but don't that as 100% cuz i did not worked on importing cars for past 3 years ( or more like 4 XD)