If your bun MUST stay outside, then could you safely hook up a heat lamp or pad in the cage for some warmth? Also, if the hutch is open to all elements, a well-insulated house is needed. Something large enough to sleep in comfortably, but small enough to keep body warmth in. If you have a barn/shed/garage then move the hutch into there to help keep the wind off.
How cold is it getting at night?
Is the water dish/bottle heated? If you have snow then the water will freeze. The nipple on a water bottle can freeze in a matter of minutes and if you only give water a few times a day then you will quickly have a dehydrated bun.
An outdoor bunny can survive, but it will never thrive. The average lifespan of an outdoor/hutch rabbit is 2-3 years, while an indoor bunny lives around 8-12.
Bring your bunny inside as soon as you can, it’s not fair to your bun to be locked out in the cold when you have a nice warm bed to sleep in…
http://www.walmart.com/ip/Farm-Innovators-Heated-Pet-Bowl-1-Quart-Blue-Birds/14660238
http://www.therabbithouse.com/outdoor/rabbitwinter.asp
http://www.therabbithouse.com/outdoor/insulating-rabbit-hutch.asp