X14 on the Genturi, too many issues with cheap CO detectors.
Onan 5500 built in is the only way to go IMHO. I know there are a ton of posts on this board about Onan carb issues. For piece of mind, I suggest using the Blue Marine Stabil at the recommended dose as well as a splash of your favorite fuel injection system cleaner. A ton of people swear by sea foam, but I like Chevron Techron and have fixed quite a few dirty carb issues with it. Use a good 15W40 diesel oil and change it and the filter every 100 hours and you will have little trouble out of the unit. When I traded my old TH in the genset had 800 hours on it and all I ever did was change oil and filters. I have over 400 hours on our current Onan 5500 and other than the fuel pump that failed shortly after delivery of the unit, zero problems since. I always use super unleaded as that is what I run in all my small engines.