tghe nest box should be lined with sawdust at the bottom, and then loads and laods of hay. Don't use any bedding, just lots of hay. You'll probably also need to use a heat source too if they are outside. Maybe something like taping a hot water bottle or a snugglesafe to the underneath of the hutch, below where the nest is (i.e. not in the hutch) can help keep them warm.