A friend of mine bought a used unit that came from Michigan. It ended up having quite a bit of rust/corrosion. He's spent lots of time treating this with rust inhibitors and painting. He had a weld on one of the rear jack fail, don't know if it was due to corrosion but makes me wonder.
I have a 2002 Monaco Windsor. One advantage is that the basement compartments are fully enclosed and protect most of the undercarriage. No rust on the inside of the compartments but the underside does have signs.
2002 Monaco Windsor 38 PKD
2005 Jeep Grand Cherokee w/5.7 Hemi