As a child, ours were out in their wooden hutch all year - over winter we'd put an offcut of carpet over the grated bit (in lieu of cage huggers!) and they were fine....
I have 2 piggies that would really benefit from being out of my living room!
Is it REALLY that bad to put them outside in a sheltered hutch? (that will be moving in to the shed when I can get the council to fix the door!)