A good ferro hull is a tough beast indeed! Unfortunately, most DIY-ers do not have the sort of tools required to bore through the hull to fit through hulls. However the hiring of someone to use a core drill is not expensive. Remember if you are using a metal through hull fitting, you must have a good barrier of sikaflex (or similar) to prevent any part of the armaure within the hull from contacting the fitting and therefore causing galvanic corrosion.
Deck fittings are a different thing altogether. If there is little perpendicular weight, or only moderate shear weight being placed on the fitting, stainless loxins or dynabolts can be used. However it is best to drill through the deck with a Hilti style drill, and back the fitting below the deck with a plate of either stainless or marine ply.
"if at first you don't succeed....Redefine success"!