TC don't make million dollars generators industry, not even saying what % of TC have space for build-in generator.
Propane carburetors are still on make-shift design level and there is no incentive to spend money on designing efficient ones.
For me front-mounted Honda EU3000, who can run whole day and more on its own tank is the best. Not only very efficient, but helps a lot with COG, so I can use empty generator compartment for other stuff.
Than for smaller loads, the $150 inverter generator from Home Depot will run whole day on couple cups of gasoline it takes.
Sure stepping outside and pull the cord is inconvenient, but at least I don't have turn the camper around -worrying about fumes entering it. ;)