Firstly, I loved the book. I've purchased several vehicle-dwelling books over the years but yours is by far my favorite. Firstly, it's packed with info. Secondly, it speaks directly to van dwellers, not those who, ahem, try to sleep in the trunk of their Oldsmobile and so on. The Internet resources you provide have made my purchase even more worthwhile!
Over the years, I've told several individuals about my idea and all have laughed it off. That said, when talking with more technical folks, the issue of condensation inside the van was brought up again and again. Over and over it was explained to me that I would wake up every morning to find everything covered with ice, or at least a dusting of frost, in colder climates.
Common sense tells me that I'd have to let my interior get incredibly cold in order for something like this to happen. In any event, in warmer climates this simply means it would get super humid inside, which, if I may say so myself, is something I'd like to avoid. With your one roof vent (and no windows, assuming you don't sleep with your front windows cracked), have you ever had any issues with condensation? If so, how did you handle it?