I have refrigerated air conditioners on both ends of my rabbit house (it is about 50' long & houses most of my meat rabbits). I also show Netherland Dwarfs, and they must be on the cold side or their ears grow too long to qualify to show. I keep them 65-70 degrees year round! I was lucky enough to find a florist's walk in refrigerator (used for flowers and 8' X 10') that needed a compressor for a hundred dollars. Grudgingly, and with much to-do my husband and his crew moved it to the house. That was 7 years ago, and I still haven't heard the end of it, but he sure is proud of our short eared show rabbits at the shows.
Rabbits just can't take the heat with their dense fur, no matter what "aids" we give them. So and indoor area (you make a coop for your chickens, why not your rabbits?) with an air conditioner is always a safe bet for bunnies!