You might consider Mg anodes also.  A zinc-rich paint would also help.

Thank you Metalguy, have you actually heard of any results from testing and use of the suggested materials??

and would the placement of the anodes be location specific??

Haven't heard of the specific use you have in mind, but anodes are used inside water tanks and to protect the lower end of outboard motors--to name a few uses.

The only requirement is that they be wet with a fairly conductive medium-the salty water in your case.  If the area where they are located becomes dry before other areas, protection stops.  The area of protection is probably on the order of a few sq. ft. per anode-just a guess here, so you'd need quite a few of them, widely dispersed.

Thank's metalguy, i will try an anode in each fenderwell and lets see how things go.

I believe that there has been a lot of experimentation with anodic protection in motor vehicles and the results have generally been unsatisfactory.  In some cases undesireable side effects have occurred including increased corrosion.  Tread carefully here as anodic protection is for totally imersed applications.  It is a different situation when you paint the metal with zinc loaded paint.  That should help.

BrianR,

Not to nitpick your good post, but the use of sacrificial anodes is called "cathodic protection".  In some cases where positive voltage shifts are required instead of the usual negative, *that* is called "anodic protection".

An example is for carbon steel in conc. sulf. acid service, at high ambient temps.  Shifting the voltage to the + side *usually* results in reduced corr. rates.

Metalguy,
Your point is well taken.  Thanks for the constructive correction.  My excuse is that I'm left handed and get many things back the fornt......

Zinks are used on marine vessels in locations that are always conductive.  Inside heat exchangers(raw water side), on outdrives, and on hull plating and on propeller shafts.  Automobiles are not costantly submersed like these applications, and therefore I doubt that zinks would offer much protection as a sacrificial anode.  Zink paint or galvanizing would probably hels, but your best bet might be the electronically controlled devices for cathodic protection.

Don't waste your time Sanjay. CP won't have any affect unless you park your car inside your swimming pool and then you would have to add salt just to make the electrolyte more conductive. Galvanizing or coatings are the only methods that will be effective for this application.

I guess that it was a poor choice of words on my part to say that electronic cathodic protection would be your best bet, because what I really meant to sya was that galvanizing or zink paint is one thing that I know will help, but that electronic cathodic protection is something that would be interesting to try for the sake of experimentation.