To make things less stressful I wouldp put a towel in there cage or room a day or so before you go. Also, take the door off the carrier and let it sit in the cage or room where they play a week before you leave. Anytime you want to give them treats put the treat in there. Or, just start giving them a carrot or parsley, or whatever treat you use in there everyday to make it comfortble. Before you put the bunnies in the carrier wip them down with the towel making sure to get there scents on it. You might even want to carry the towel around for awile or use your shirt as the towel. Then it will smell like you, a comforting smell in there carrier and they won't be as stressed.

Ash