Does anyone here keep ferrets? I have a question about winter insulating?

It may seem like an odd question but I’ve heard they are a popular pet in the U.S. aswell. I have two ferrets (pets not workers) they live outside in stacked hutches. We apparently get harsh winters in the village I have moved to (in England) and I am worried about the cold. They do kick out alot of body heat and I know they are pretty sturdy creatures, but like I said it’s getting bloody cold already, clear nights and frosty mornings and it’s only November. Does anyone that keeps ferrets insulate their cages? if so how? and do you think it’s something I need to do? I can buy hutch covers but they cost a fortune and they don’t seem very good. Any advice would be appreciated, I really care about the welfare of my woozles. Thanks.