I'm glad you two brought this up. I didn't because I was so focused on squeezing in tips on campsite selection. 

Carbon monoxide poisoning is a major concern if you're winter camping. I have a singlewall two-person winter tent that I always fully vent out and partially unzip before sleeping. Same goes for my three-man doublewall in winter. I don't use a stove for warmth, but cooking always happens outside the main tent body. Friends had a close call one night and woke up lightheaded — thankfully, it didn't go farther than that, but still...

I'm very, very glad you brought CO poisoning into the conversation.