Disadvantages:
Corrosion pitting and hull degradation is imminent especially in salt water and where steel fasteners are used
You're likely to dent it
If it's strong enough to resist denting, it'll be heavy
Repairs are either inboard lap patches which would be hard to install/require engine removal or external lap patches which would create drag and change handling
Welding is not an option or you'll crack it around the weld
Repairs require more specialized tooling that cost $$ (composites requires sand paper, resin, a brush, and fabric while metal repairs take a drill, drill bit, pop rivet gun, pop rivets, sealant, metal cutters and grinders, and metal benders depending on thickness)
Man hours to fabricate such a hull by hand would be enormous making the cost of a hull extremely expensive and likely to exceed a carbon fiber hull
Advantages:
Engine, pump, midshaft, etc mounting is easy as you can drill and tap the hull instead of extra fittings
Serious cracks and be repaired on the beach with a drill, pop rivets, and a beer can but must be sealed and properly fixed later for longevity