Some good answers here. After reading them, I will keep the fly door open on my next trip and see if that makes for less condensation. There are vents in the fly, but probably not enough.
My previous winter camping experiences have always been in a shelter with one open wall, so condensation was not an issue.
I imagine an unheated trailer will have the same issues as a tent, seem to remember something a few years ago about some guys sleeping in a trailer without a working furnace and reporting the condensation issues in the trailer.