Abi, don't worry my lovely, I had outdoor buns who were outside in ALL weathers (even snow!) and lived to be over 10 years old! (they also lived alone).
Make sure Riley gets lots and lots of extra bedding to snuggle himself into. He'll be fine. Eddie used to have all of the extra bedding, but still preferred to sit out in the cold with his hay in his tray...:roll:
Buns eh!?!