There are four or five places around the Country that sell used parts from RVS.
An onboard generator is far more friendly than an outside unit that you have to go out to start, fuel and secure and store when moving.
I can't see what RV you have and if gas or diesel, but if you can afford 7,500 kw to 10,000 kw in portable generators you can afford a new Onan and most certainly a used Onan which while outside the RV can be fully serviced with new belt cooling inspection etc.