If for some reason he gets very excited, be ultra careful to not touch his tail. In my dozens of long drives to a good vet the pant-leg option caused no problems.
But it's escape -roof, shaped like a sausage which is easy to pick up and carry. Your ig will see no disturbing sights, so the net effect will be he is much more calm at the end of the trip.
His tail needs special gentle care because it's exposed.
When I watched the "Life of Pi", I realized that animals can get motion sickness. I don't know whether iguanas get motion sickness. It's true that other animals do. I just assume igs do also. If I were planning a multi day road trip, I would ask my vet for some kind of sedative given in a light dose, for the driving parts of the trip. But on the other hand, your ig will not get hurt or die from it.
Good Luck and happiness,