I have a 2014 Winnebago Sightseer(gas) with a Onan generator. It's been awhile since I started it(maybe 3 months)....all of a sudden when I try and start it from the panel in the coach, it turns over ...
If it was running before you stopped using it, then the carb is probably gummed up. If you're handy with tools, it can be taken apart and cleaned. And from then on, use Sea Foam in your gas tank and make it a habit to run the genset under load at least monthly for about an hour.