How to keep rabbits warm in winter

From Pet Encyclopedia

I have 3 rabbits all boys. 2 live together the ofer lives on his own the hutches I've got are chicken coops they are very big I tried to get a pic on but I don't know how. Any way we were thinking on getting a thermal coop cover that fits the big hutch and chuck some old carpet over it. Plus we don't what to do with the smaller one. I can shut them up in there top house but then they won't have any water. I need some help please.