So, what are you shooting that doesn't have a rib? Few guns were ever made sans a rib of some sort.
The corrosion issue seems to be more common on guns that have a brazed rib and under rib, rather than a silver soldered rib. Might be the higher heat involved, but, I'll let others with more training pass that judgement. My 28 gauge Darne V19 has no under rib, inspite of having a raised rib, and there simply isn't much space for any corrosion to form, and, I would see it if it were to occur. There is simply a void under the barrels.
I own a few pumps that have no rib, no corrosion there, for sure, but, no caché, either.
Best,
Ted
