I think they travel better in a snug dark box. If they have room to stand they're always shuffling around trying to keep their balance every time the car starts/stops/turns. It's better if they can just nestle down in some straw. If the box is dim/dark they'll just doze until they arrive, they won't need food & water for the trip. Then you don't have to worry about water tipping out & splashing all over. They should be able to nap during a 3-hour trip and wake up on your arrival.
Just make sure they have sufficient air in their box, and of course NEVER leave them in the car with the windows rolled up. But you knew that already.
Bon voyage!