Hey, cardboard is no match for the cold- I'd use the ice chest- just put a small wad of tape in the opening or on the lid, so it doesn't shut tight. I went thru a 4 day power outage from an ice storm with about 3 snakes (bagged) in each large ice chest, & only opened about every 8-9 hours when I changed the water in the bottles. Also, 85* is pretty intense- your goal should be about 80*. None of my snakes got sick or harmed in any way from that ice storm ('09) -I had 15 at the time including a large BCI. Now I have 19 snakes, & I would do the same thing again if needed. Save the blanket for the outside of the ice chest. In the ice storm I went thru, I put all my ice chests together on the couch, & padded around them with pillows & blanket. I often wished I could have fit inside one of the ice chests myself...My house got down to 45*, by the way. And in each ice chest, I used 2 jars of hot tap water (not boiling). Air goes right thru the pillow case, just make sure he's not right up against the hot water bottles- wrap a small towel around each one, in case he moves around in his pillow case. Hang in there.