I would say as long as they are potted and you have them inside a vehicle they will be fine. Remember to not leave them in a closed vehicle (with windows) in full sun. That's a bit much for plants, too. They won't know they have been moved if you don't tell them. ;O)

also, remember to subject them to full sun gradually once you've gotten them out. Maybe an hour, then 2 hours, until they are strong enough to withstand our weather. Try to find a shady spot and don't plant anything until it's settled down a little while and is looking strong. Then plant it in the appropriate exposure for it's type. And right, watch out for roasting them behind car windows.