The key things to remember in the winter are:
Water: Water freezes when it gets cold. The water bottle in the Eglu is insulated from the cold but if it is extremely cold there is still a chance it could freeze so you should check it everyday. A good idea for the winter is to have a spare water bottle so that instead of filling the old one up you can swap it with a full one. This way the rabbits have an opportunity to drink and you are less likely to crack their bottle when trying to break the ice!
Food: Don\'t be suprised by your rabbits eating more in the chilly months. They are using up lots of extra energy to keep warm. Keep an eye on their weight though to make sure that they aren't pretending to shiver when you are about so that they get extra treats!.
Warmth: Unlike other houses the Eglu will keep your rabbits nice and warm in the winter because its the only house that has all round insulation. Make sure that there is always plenty of clean bedding.