The longest I have ever driven with mine was about 40-50 minutes. But I’m currently trying to bond my trio. One would continuously mount the other and it would start a fight. So I decided to start doing car trips to help stress bond them. I did it for about four days. Just the two who didn’t get along the first two days, then all three the other two days. I put them all in a cat carrier. I made sure they didn’t have enough room to start a big fight, but at the same time I made sure they had enough room to be comfortable. Today was the first day that I stopped the car trips. I had them all three together in the playpen in their usual bonding area. Domino, the one who would mount Oliver and start fights, didn’t mount him once today. I’d say that the car trips did a pretty good job for my bunnies. You could start trying to bond them now and then when the car trip comes along, put them together for stress bonding. Three weeks might be enough time for them to get comfortable with each other, and then the car trip might help bond them even more. Though, if you won’t have someone sitting in the back, or wherever you’re going to put them, you might put them in separate carriers, besides the two bonded. You wouldn’t want them to start fighting in the middle of driving and not being able to stop it right away. Although I sat with mine in the back while we were driving, they never started a fight. I think that the car trip helped Domino see that Oliver wasn’t a big threat, because now he seems more comfortable with Oliver.