Its the same temperature as the stables?Yeah you are probably right. When Monster was alive we had to build them an outdoor shelter - at the far end of Storm's field as it was the only place they were safe from his marauding ways!!!
Its cold in the garage at night more than ever lately though - I go in to say goodnight to Husky and I wear my coat over my night attire!
Maybe pop down some cardboard, then some straw under their blankets. That's insulating.