Regarding CO posioning, gas engines produce more CO than diesel, because CO is a byproduct of incomplete combustion.
Since diesels get all the air they need, they don't produce as much CO.
But truckers have died from CO poisioning in rigs too, look it up. And I suspect a number of deaths in sleepers have been wrongly classified as natural...
Furthermore it is an old misconception that engines doesn't suffer from idling, they do, and more than from being used. look up cylinder glazing.
Lastly - to me - its seems very wastefull and bad stewardship of nature and our ressources to leave a truck idling all night just to have a bit of A/C running.