I would definately bring them into a garage/shed/porch at least at night when it's winter.
This may not be the best idea because temperature fluctuations can cause illness. The rabbits need to either be permanently in and out. Going back and forth is not generally recommended.
Aside from that, the most important thing is to have a winter hutch. This means absolutely no all-wire cages. I know these are sometimes advertised as "hutch-kits", but they will not work.
During winter, your rabbit should be in a hutch that is at least 3 sides solid wood. The best all-year hutches will be half wood and half wire on the front side too, to "enclose" one end of the hutch into a little run-in box. If you do not have a shed that is exactly like that, I would suggest building your rabbit a wooden box that will fit in the hutch. Fill this box with lots of hay or straw. Clean it out often, but make sure it's always full.
I am in PA too and our winters are pretty mind for bunnies. As long as they have an enclosed hutch and a small, tight box with hay inside to keep warm, they should be fine.
A heavy canvas tarp can be nice to drape over the hutch at night to keep some heat in and bad wind out, or even on especially cold days as well. But on sunny days, you shouldn't need it.
- The rabbit MUST stay dry. Rabbits can handle the cold well, but not if they are wet. They will chill and freeze easily if wet. So make sure the hutch is well insulated and high off the ground, away from any snow or other precipitation.
One thing to check frequently is the water. It is easiest in the winter to use a crock which you can switch in and out as it freezes and replace. While the water inside a bottle may not be frozen, the little metal nozzles can freeze shut. So you may think your rabbit has access to water when he really does not. A crock is best.
I would also up the protein in your feed. If you are someone who does the timothy pellet/timothy hay diet, I would recommend switching to an alfalfa pellet for the winter. A pellet with 16-18% protein is preferable, and it helps to sprinkle some oats on top of that too. Protein and fat levels are important in the winter for giving the rabbit's body energy to keep itself warm. Just make sure you make this change gradually, as a change in protein level can cause illness if done suddenly. Changes in protein can also cause a molt, so I'd suggest getting the rabbit on a higher protein food now, before winter hits, so that they have a coat of fur back on them by winter.
Hope this helps!