Metal spraying to repair rust pin holes?

How bad is the area you are wanting to fix ? Photo ? I'd me more inclined to fix pin holes in a floor with epoxy and fiberglass cloth from the interior and shoot undercoat on the underside to seal it up after I brushed on some epoxy to stop any water from getting under the repair. You are never going to see this stuff,it will probably last over 20 years or more depending on how you treat your ride( driving in rain,storing the car outside) If you keep it dry for the most part it will out last you and be invisible if done right.