Show bunnies do it all the time, not a problem!
Suggestions:
Put him in a small carrier to travel. I know it seems like they should have a large carrier or cage on trips, but this is not so. Most importantly, a small carrier acts as a seatbelt. If you were to have an accident, it would protect your bunny better than a large enclosure where he could get thrown against the bars and suffer injuries from impact. Also, rabbits definitely stress when they're in a car. So a small, enclosed area feels much safer to them than a larger one.
With that said, bring a harness and lead or a little playpen to set up so that your bunny can run a bit and stretch his legs at your rest stops.
Make sure your rabbit has fresh hay available at all times. Having this to chew on really helps entertain your rabbit and keep his stress level down. A veggie or two here or there would be ok as a treat to keep him interested, but try not to feed too many fresh veggies/fruits on the ride since their systems can be upset from the stress already. A dry, high fiber food (hay) is best. Then you can slowly start pellets, veggies, etc., up again when you reach your destination.
Make sure the rabbit has fresh water available at all times. You may even choose to buy a jug of distilled water and use that the whole trip. Water tastes and is treated differently from place to place and can make rabbits sick, just like humans with sensitive systems. But you can buy distilled water pretty much anywhere with a Walmart and this keeps your bunny on a consistent water supply the whole time.
Make sure the carrier is out of direct sunlight and doesn't get too warm in the car. Sudden change of temperature is the biggest risk to adult rabbits. Keep the car about room temperature for safe travels.
Hmm...that's all I can really think of right now. I hope this helps!
