I'm a firm believer in frost cloth or any other covering that might do the job. I've never had real cold hardy succulents but the "minimum of 50 degrees" plants that I own are outside covered with their cloths (shade cloth and N-sulate cloth) and I'm hoping that the nites of upper 30's temps don't do them in. So far, so good. I am in California now but when I was in high altitude desert, these 50 degree plants were inside a pumice concrete building.
I'm also more of a container gardener and someone recommended that if I was planting a new plant, that I should line the pot with trash bags (but leave the bottom and drainage hole uncovered) before putting in the soil. Tried it with a couple of pots and the plants survived thru a winter on an elevated open deck in Spokane, WA.
