CO is very similar to "air" in weight. But given the choice your lungs choose carbon monoxide five-to-one over oxygen for absorbsion into the blood. It is most definitely NOT a head to head contest.
One single RV isn't an issue. It's when there are sixteen RV's per acre all running a generator. I heard CO detectors going off all over White Wolf campground in Yosemite. Another time detectors screeched in the US Forest Service campground, in Lee Vining canyon.
People scream about city smog yet may endure ten times the amount of pollutants in a packed rural RV campground. To say doing so is not absurd, is -stupid- incarnate.
I have four white enameled boards vertically mounted three feet away from my Kubota's exhaust. Weekly glances tell me which way the wind is blowing. If it should come from the north I avoid starting the engine. Time to wait.
