I've seen Onan 7000 watt generators installed on trailers intended for police use that were mounted well enough that they were quieter than inverter gensets. It is all in the shock mounts, isolating exhaust and intake hoses, slapping a resonator on the exhaust, and other items which a lot of RV OEMs skip on.
Now, if Onan could make a four pole (so 1800 RPMs are needed, not 3600), oil pressure lubed (not splash lubed), variable RPM inverter model with a battery (perhaps a supercap) to absorb an incoming load spike until the engine could spin up and take the load, that would be almost ideal.
