first off Duncan is SO cute!

Keep a lot of hay in with him, be sure to check it oftern to make sure it is dry. Cover all of the open sides of his pn with a insulated plastic. and if his hutch is big enough you can put either a warming pad or a heat light in there with him (JUst make sure that he can not get to any of the wires because bunnies like to chew)

Here is a wonderful website I found about rabbit winter care.
Winter Care