Mine live in an unheated shed for the winter. I think I am in 8b?
It gets COLD out in that shed. Only a little bit above the outside temp, and they are usually just fine and go dormant very thoroughly, no etiolated growth for years now.
I have lost em all in the past when we had a crazy hard freeze and they all froze solid, this was when I lived in a tiny ramshackle cabin in the woods, off the grid, only a woodstove for heat, basically the whole house was an un-insulated shed. I got home and they were all frozen solid, so I frantically cranked up the woodstove and then got really sad as they one by one thawed out and flopped over into goopy piles. If they freeze just a tiny bit however I find that they grow with exta vigour and often gain a lot of girth the next growing season. This year in the shed I just hung a heat lamp over them like I use for baby chickens and left them in the shed while we had outside temps down to the single digits and they were fine.
Those were funny days tho back in the cabin. The cacti occupied about 50% of the available living space that I had in there all winter, I kept a Brugmansia tree in there with me too. We all got really close.