I would put them in the truck, or is there not a truck involved?

I would take them out of the pot and wrap the root ball up in a couple layers of plastic, like garbage bags or something like that. then you don't need to worry about soil getting all over your car. You'll still need to prop up the plants by the stem so the branches don't break off. Maybe some flat cardboard boxes will work for that, something that can reach the stem between the branches will be necessary.

Don't need to take them out of pots. You can use scrunched up newspaper to surround the trunk of the plants on top of the soil, even bubble wrap. Then tape it down a few times across with packing tape. Put the whole pot into a garbage bag and if you are still concerned about spillage twist the ends of the bags at a couple of points and tape down again.
That takes care of the pot end.
For the growing end, it depends on what vehicle you are intending to use. and how much other stuff you have in there that might damage the leaves etc.
If, for example, you were thinking of strapping to a roof rack, well you'd position the pot at the front of the car and try to wrap the rest in as much bubble wrap as yu could afford.
If inside - like in the boot (trunk?) and then laying some seats forward, you just need to cushion the plant with bubble wrap, blankets, whatever works to stop it bouncing around. Seatbelts can work for plants, too!