Generator doesn't supply power to air, microwave, in cabin

What is your fuel level now? Most RV generators are connected to the tank such that their fuel pickup only goes partway down the tank, and they won't run typically below around a quarter tank.

I would tend to suspect a fuel problem of some sort before the spark plug on the Onan generators. That seems to be more common. Spark plugs also don't tend to die suddenly, in my experience, but gradually the engine runs less and less well.