I've had outdoor rabbits for 12+ years, and I live in the frigid north, much colder than by you, so hope this helps.
It's not the best time to acclimate an outdoor rabbit, especially notby taking in and out, but it can be done. If a rabbit is outdoors as itgets gradually colder, he learns to adjust--conserve body heat, build anest, etc. etc. They actually need to learn how to build a snugburrow--something males don't do in the wild (see Watership Down
).
If you
possibly can, wait till spring. If you can't, try this:
An outdoor hutch should have two parts: a wire section(big)and a box section (not too big). The box area should bestuffed with hay or straw, then
you make a little burrow in thestraw just big enough for them to turn around.They won't knowhow to do it themselves, most likely. Keep the door of the box just bigenough to get through (will reduce cold air). Don't forget to remakethe burrow until they learn not to smash it down. It may take a week ortwo to teach them.
The biggest problem is they make a mess to mark territory. Obviously,you don't want the box wet with pee. It may sound harsh, but I actuallylefta box messy and wetwhen training a young buckto keep warm in winter. It took two days, but he figured it out andhasn't messed since. He was a strong healthy young boy who'd alwaysbeen outside, but he was on his own for the first time and good habitsare vital.
Make sure not to put food in the nest area. They must know that they
do not eat or go to the bathroom in the nest--it's only forsleeping. The wire section is for food and bathroom and exercise.
A tarp is great,asit will cut down on wind, butmake sure they get some daylight for a little while in the sunny partof the day. You can throw old quilts, etc. over the top for insulation,and snow will help too.
All mine have survived many -20F days, and often without so much as achilly ear. I go out on cold mornings, shivering, to see them bouncingmerrily off the walls. An older sick animal may need to come in, but ahealthy rabbit doesn't necessarily feel the cold like we poor fragilehumans with no fur coats.
If your rabbits have always been inside, they will not have grown atrue winter coat. That's why I recommend waiting til spring, so theycan go through a natural cycle before next winter. They will be at adisadvantage without the heavy winter coat.
Good luck. I hope you can wait till spring, as that is the best time to introduce rabbits to outside.
Rose