I may have missed a post or two, but the thing to keep in mind about
electronic rust protection is that it requires a electrolyte to work.  In
the case of the ship the ocean is the electrolyte and completes the circuit
between anode and cathode even if they are seperated by some distance.  The
problem with using this process on a car or van is that there is no
substance to move the charge through.  The corrosion of steel in air
involves small charge imbalances in the sheet of steel itself.  Water that
condenses on the steel allows charge to flow from one area to another.  In
the case of a car the distance traveled by the charge can be minute, say
less then 1/100th of an inch.  A sacrificial anode bolted to one end of the
car simply can't protect the other end, because in air it is never
connected in a circuit with the other end.  This is why zinc coatings work
to protect steel, they are all over the metal and can protect the steel
even when the galvanic cell set up by water on the steel is very localized.
 but if you had a big enough hole in the coating of zinc say 1" the steel
in the center starts rusting.

Dave K.