Interesting bit of trivia: at -40 it's not necessary to specify C or F, that's the point where they're both the same.
When I was a kid in the boy scouts, they had an award they gave out when the total low (with wind chill) on the days you camped added up to -100F. I got the award one weekend - one day was -60, the other was -40.
Obviously it's -39, and since -39C and -39F are different you'd now be required to specify. If you knew which scale the 1 degree was from it wouldn't be difficult.
Below, is super important.. I use closed-cell mats designed for winter camping and carrying in the backpack.
Somehow I don't think the cats would work so well under the sleeping bags..