#1 Doesn't matter, just like the cold making it up into your room fumes will do the same thing.
#2 I am not just talking exhaust fumes. Fumes from that plastic gas tank for the lawn mower, cans of spray paint, glues, oils, all put off fumes and do leak, especially in warm weather.
I am not saying it would ever be enough fumes to hurt you, but it is something I know I would never want to have right below my bed at nights. Esp when we are talking about my kids or anyone else in my family.