The Honda and similar generators run very clean, but they still emit untreated carbon monoxide. I'm not so worried as Soundguy, and I would have no problem sitting the generator on a trailer tongue, but everyone has to find their own comfort zone when it comes to safety. As I said above, I don't like to run mine with the exhaust outlet under the slide. Slides are far from air tight. We all have CO detectors, mine has never gone off from generator use.
Portable propane heaters are a different animal, and the catalytic grid burns CO so completely that they are okay to use indoors, with ventilation to provide oxygen. I have one which I have used quite a bit in a tent, and felt safe enough. I don't like them in the tighter trailer box, but there again, that is just me finding my own safety comfort zone. I also don't like the water vapor they create. Regardless, they are considered safe as far as CO is concerned, as witnessed by the fact that everyone's CO detectors don't shriek.
Try running your generator inside the trailer, just for a test, and see what your CO detector does. ;)
