Anecdotally, I`d hazard a guess more boats than not around 35 ft and up have a built in generator. Including gas powered boats with gas gensets. Perhaps the proportions have changed as more boats opt for solar/wind and battery banks to suit.
If you go the standalone gas not inbuilt route, you have to store a supply of gasoline onboard. Many do that for outboards already, but mine is on kept on deck lashed down, and is a lesser quantity than you might need.
Where you locate it, for air intake, exhaust, air cooling,and weather protection will need resolving.Some people carry a Honda as back up to the diesel genset.
I think that, for good reason, most boats go with the inbuilt diesel genset. You can make it quieter by opting for the soundshield, even fit an exhaust gas/water separator. It`s likely your boat has a place one can go, perhaps even a place one originally went. Install won`t be cheap but once done it should be rewarding. Sizing is a consideration, your electric kettle may like ours draw 2000watts,if your genset is 4KW that`s a big,if brief,power draw.