We used to have a bunkhouse trailer so no built in genny. We bought a Yamaha 3000. Great generator. Still have it. It was fine for boondocking at motocycle races. Not so convenient for overnights at Wal-Mart, truck stops, etc.
Just bough toy hauler. Onboard genny great. Runs everything, no issues. Great for overnights on the road. Uses more gas. However, I still carry the Yamaha. Fuel efficient when we don't need both A/C's.
You may want build in so you can cool coach when driving. Dash air probably not enough.