OP - since you are a FF, you probably know the real reason that CO is so deadly and it is not the reason mentioned above.
That said, every heartland factory installed genny has exhaust exiting from under the left side (there are a few SOB toy haulers that exited the right side).
Most of the HL's exit between the slides. I'm pretty sure your 310 is the same as our Cyclone 3010, exiting between the slides but under a basement door. Was never crazy about that.
There is a reason building codes require all "flame" devices exhaust a minimun of 5' from any opening or window in a buiding.
The factory installs "use" to come with a chrome tailpipe extension that pushed the exit out past the sidewall of the trailer.
- I have to switch to my iPad, I'll finish in a bit -
We are on our 6th season and only twice did the CO detector alert. Both times was after 8 or more hours of use and both times overnight. One occasion I attributed to our being parked next to a steep slope. The front of the trialer was very low to the ground and the left side had a hill the was well above the roof of our rig.
The second time was during a 100 degree stint at Dover speedway with zero breeze.
I have since added a Genturi pipe extension to put the draft above the roof line. FYI, with Genturi you will most likely need the 18" extension to clear our roofs.
Two notes, Bohemian mentioned extensions are not to be used. The manual is referring to extending your tailpipe with hard pipe. The Genturi has an air gap between it and the genny exhaust. This just pulls a draft and redirects the exahust up over the roof.
I do use an 18" extension on occasion to just assure the exahust is clear of the rig.
Hoefler mentioned plumbing all the way to the rear of the trailer.
I have considered this a few times. If you search online you can find a calculator to determine what size pipe is needed based on the length of run and number of turns (90's).
Onan, although diffulcult to find, does list the exhaust requirements as far as piping and back pressure requirements are.
You are right to be concerned, regardless of burning .8 GPH on propane or .6 gph on gasoline, both scenarios produce CO.
Open windows (obviously away from the exhaust) are your best bet along with a properly operating CO detector. Besides the factory installed hard wired 12 volt detetor I alos have a battery powered hosehold type.
And of course, if really concerned, just don't do it.