I keep my entire rabbitry in the basement, which is currently comprised of my meat rabbit breeders (two meat mutts and Flemish Giant) and my English Lop show rabbits (2 bucks, 3 does). I usually have at least two litters of kits down there, which can sometimes bring my numbers around 25-30ish. Mine is partially in-ground, so I experience temperatures that are usually between 60-70 degrees year-round, though there is some fluctuation in extreme weather conditions. I live in southeastern TN and it's notoriously sweltery here from about May until September, so I keep a dehumidifier going 24/7 during that time. I'm also considering a window AC unit for the basement to cut down on the "swimming through the air" feeling that comes with southern summers.
I am extremely fortunate that my basement is equipped with a roll-up garage door. I thought it was stupid when my husband and I originally moved into the house in 2013, but I quickly began to appreciate its value when I began my work as a "rabbiteer." It's so convenient when it's time to clean out cage pans and move the "bunny berries" out to the garden, or when it's time to restock the feed and hay supplies. Plus, now that it's starting to cool off, I can roll the door up to get even more air circulation down there.
I do, however, find that you have to be super-vigilant about cleaning up after your rabbits so that things don't start to get a little funky. When I first began raising rabbits in the basement, I was cleaning pans almost every single day to keep the smell down. (Now, to be fair, I have an extremely sensitive nose and am sometimes bothered by smells that don't phase other people.) I now use Sweet PDZ and pelleted horse bedding in each of my cage pans to neutralize the scent of rabbit urine and increase absorbency, which allows me to go about 4 days before needing to completely dump and spray out the pans belonging to my breeders and show buns. I'm still dumping the pans underneath my grow-out pens every 1-2 days because growing kits produce an astounding amount of poop.