I have some Lewisia that have overwintered for several years, they are are in a bed of sharp drainage (2 parts coarse sand, 2 parts pea gravel, 1 part compost) and sempervivums. The only thing I do for the winter is place plastic netting over the bed to keep the squirrels and chipmunk out. I put a small layer of oak leaves over the bed vs ground up leaves to keep the retention of moisture down.