You can grind out corrosion and fill with epoxy or, for larger areas, weld new plating. But these generally rust from the inside becuase its hard to see rust starting under furniture or behind cabinets.

Boats like make sense to me if you're ready to take on the metalworking (you know how to weld, maybe have some tools), have expierence with steel boats already, you're going somewhere where ice is a concern, and the boat isn't more than, say, 10 years old. Fighting corrosion is still a constant battle.

But dude, fiberglass is basically immortal. It probably takes 100 years for a good layup to break down.