I have many camellia japonicas and sasanquas. In very cold weather I protected newer smaller plants. But global warming has dealt a bad blow to E TX , we had +7 °F overnight and in the 20's °F for 4 or more days. Of course the blooms are gone (have some flower phots with 2" of snow on the bloom). Meaningful covers on 8' tall 12' long plants is not rational, so I am waiting to see what is left. Literature give references for 32 °F or 20's °F for a few hours, but not 7 °F. Any guesses?
Some camellias can survive in zone 6 (0 F) but I think it rather depends on the variety. Best to wait and see; in the worst case you may need to cut back to the ground. While air temperature may go to +7 likely within a foot or so of the ground the temperature will be higher. On the positive side it will be a good indicator of weak and crowded growth that can be thinned out. Lots of pruning work to be done in the South this year I think.