We do it all the time, that's what having an Onan is all about. They are heavy duty and designed to handle extreme running conditions. We have put over 1K hours on our unit over the last 9 years and it has never let us down no matter how cold or hot outside, from sea level to over 9K' elevation it just cranks right up with a press of the switch. Always run with exterior genny door closed as it is vented to Onan specs, plus it greatly cuts down on sound emitted from genny. That is what works for us, but I don't see anything wrong with leaving it open either if somebody believes it helps with cooling.
We use Stabil when adding fuel and a bottle of Seafoam maybe twice a year, have never experienced a carb or fuel delivery issue and all we use is the cheapest ethanol laced fuel we can find as we do with all of our motorized vehicles. We have a genturi, but it's rare we use it since all of our camping off the power grid is dispersed with no one around, plus we primarily boondock in the 4 corner states where there is always a decent breeze if not outright windy. Only time our CO detector ever went off is when we had the window directly over the generator open to disperse smoke from the galley where my DW got a pan too hot and oil started to smoke.
Nothing makes an Onan happier than to perform it's job as often as possible, letting it sit unused is detrimental to it's overall reliability, and in turn can lead to several issues that have been outlined on this forum countless times. We also do lots of cold camping and run a couple of space heaters as well for a few of hours before bedtime, really gets our rig nice and toasty before we go down for the night. Normally by 5am the rig is getting nippy inside and I just press the switch to get her purring and head back to bed for another couple of hours. We thought we might not utilize the genny much when we first purchased our TH, on the contrary it has allowed us to be 100% self sufficient making every adventure off the power grid virtually worry-free.
