Having used generators to supply power for week-long power outages due to hurricanes here on the Gulf Coast, I would have no qualms about running a generator overnight unattended in terms of overheating. Carbon monoxide is a real concern and has caused fatalities due to generator operation in closed spaces in these situations. If you are running it in the truck bed below the overhanging bedroom of a fifth wheel, I'd be concerned. Better to secure it outside behind the trailer. If you have a built in generator with a properly designed exhaust, you should be OK.