Would this be a Red flag in your book?

[Charlie 5320]

I bought a 98 Daybreak in MI. Last year and it was loaded with rust and some was falling apart. Ended up selling it, not something I wanted to fool with. I bought my Dolphin in northern IL a couple months ago and it's like new underneath. So it does depend on how they were driven.

[Dtwallace]

Most of the response you've gotten to leave this project could be a good one.
How ever we can't see the conditions you see, and surface rust is not a deal breaker at all.

As mentioned in one response, storing the coach on an open lawn will in some cases rust a sparsely coated underside. I've witnessed this first one my coach, it's a 2012, and no winter salt has ever touched it, and the rust I see on the frame reminds me of a vehicle that has been on the road for many more years.

Some RV's are not as protected from the factory as most of us would like, so we have to do more ourselves, like more spray on under coating.

I would suggest a closer inspection of the rusted areas with a welder's pick hammer.
Tapping on the rusted area's will give you an indication of whats behind the rust.

DTW