How old are your bunnies? I have outdoor rabbits, and at times I would let them go in and out of their hutches at will. They were adult rabbits and never got sick, but their hutch was filled with hay, so they could dry off, when they chose to play in the rain. My rabbits would also play in the snow, but the colder it got, the less time they would spend outside of their hutches. If you are worried about your bunnies, then perhaps they should be locked inside of their hutches during bad weather. I don't know what kind of predators you have in your area, but that would be a huge concern. I would keep them in the hutch during the night, when most preditors are out. If you have hawks or eagles, put some bird netting over your garden. If there are foxes or dogs in your area, you may need to do more preditor proofing.