At our races, we would run two ACs all night in the wicked southern humid heat. As per my dealer's recommendation, we would always leave the door closed. The way its built, the design is supposed to help it cool better with the door closed. At least that's what they told me. But never a problem for hundreds of hours.
The only time we had problems with fumes was when we had to lower the front end of the camper to get it level. Twice, we had to lower the front end quite a bit to get level and both times, we were awakened around 1:00am by the CO detector going off. I had to put a fan underneath the camper those nights to blow the fumes away but after that, we never picked a spot where we had to lower the front.