The only truly quiet generators that makes 240v are the Honda EU7000 or the Yamaha EF6300, they are both over $4,000. They are a magnificent generators, just heavy and expensive for "portable" use.
If you don't really need 240v (which you likely don't for an RV) then just about anybody's inverter generators in the 2,000 and 3,000 watt range can be connected together with the proper parallel kit.
There are no generators that are not inverter types that I would consider quiet enough for a campground. Even the quiet inverter generators are bothersome if people run them for hours on end.