I have grown alpines in containers for many years and prefer to grow them that way. They are very hardy. They were originally discovered high in the Swiss Alps. Plants that are well established in large pots need minimal protection. One option is to move them into an unheated shed. What I do is put a little fence around them making the enclosure at least 6″ larger than the pots and about 6″ taller. I then fill the space around the pots and on top of them with straw. Some people wrap their plants in bubble wrap or black roofing paper. I don’t advise that because both of those materials can cause heating and a freeze thaw cycle. All they need is some protection to moderate the temperatures and cut down the ups and downs.