I sure wish SOMEONE would design, manufacture, and offer a build-in-able 4000 watt, gas powered, 1800 maximum RPM at full power, inverter based generator for RV manufacturers to install in their small gas powered RVs.
I'm sure it wouldn't take rocket science to do so ... and I for one would spend more (over and above the approximate $3K adder for a current 4K Onan) for the option when buying a new RV.
Imagine .... 4000 ultra-quiet watts on tap whenever wanted/needed anywhere anytime ... at maybe a 54 dB or less noise level at full rated output. Nirvana!
For what it's worth, this is the closest generator to what I describe that I've been able to find available so far noise-wise and power-wise ... unfortunately it's water cooled:
http://fischerpanda.com/fischer-panda-dc-agtpm4/