As you very well may imagine, it’s an RV generator that rests in your RV instead of being placed outside. However, it’s not all sunshine and rainbows. Onboard generators are noisy as hell (especially when it’s bouncing around inside that little cabin) and produce heat, which is counterintuitive if you plan on running the AC.
In short, they’re not worth their weight in gold. The main purpose we see is if you go to an RV park or camp that has frequent - and rather close - visitors, and you’re trying not to disturb them during the night. Portable RV generators are the choice of full-time RV-ers for multiple reasons, including cost and maintenance versus an onboard generator.