I'm not saying that steel boats cannot rust from the inside only that I have experienced more problems out than in. The cabinetry is definitely an area of concern. On Raven none of the cabinets are lined at the back. Inspection of underdeck is a bit of a pain because of headlining and insulation but I doubt that is one of the problem areas. More likely are surfaces where moisture can collect.
Have to agree in general that modern steel coatings have reduced much of the maintenance required. I am quite surprised by how little maintenance has been required with Raven.
Re the streaks , we have an Alejuela 39 on the mooring next to Raven and she weeps rust stains from her chain plates and stanchions as badly as anything on Raven.
Inside, we have kept a constant watch and have only needed to paint one small area where a fresh water inline tap had been rubbing against the hull.
The problems outside invariably start with impact e.g dropping a metal winch handle onto the deck is not a great idea even if you catch it after the first bounce and before the final splash.
In fact the biggest bummer with Raven is that her topsides need recoating.
Having to do this by brush may be beyond my skill as a painter. To have her sprayed is going to be a right pain in the bum, not to mention the expense.
“Give a man a fire and he's warm for a day, but set fire to him and he's warm for the rest of his life.” Terry Pratchett