I've only done this once earlier this year in Feb or March winter camping. The average high for the day was 19° F, probably around 0° at night. I did make one slight change to the plain 'ol hot water in the Nalgene though. I added a half pack of Jello. It was amazing! I drank some hot Jello before I went to bed, then tossed the bottle back in the bag. In the morning it was cold, but I got to eat Jello for Breakfast! I'd imagine it'd be easier to eat if you had a soft sided container, you could just squeeze it out! Granted I'd never do it during the spring, summer or fall due to the much higher probability of dealing with a bear.