Im an auto sparky working in mining and this is a huge problem with exposed wiring and non sealed plugs/connectors. to me the number one way of preventing it is maintenance. every couple of weeks check your wiring check your plugs etc, keep them clean. clean all connections out with contact cleaner and use some good quality electrical grease on all connections to prevent that salt water getting in and green death occuring. If there is some green death in a connection ensure its cleaned out as i believe it grows.  If you make a connection use some dual wall heatshrink to protect the connections. And also make sure everything is washed down with fresh water to get that salt water out and prevent the initial corrosion started. while this wont prevent it from totally happening it will help.

grease: http://www.ebay.com.au/itm/like/261453385338?limghlpsr=true&hlpv=2&ops=true&viphx=1&hlpht=true&lpid=107&chn=ps

Cheers Joel

 Plenty of lanolin spray works wonders behind my dash.  I dont use it on sounder or gps connections though as dust and crime can stick to it.

+ 1 for lanox

Goes on all my wiring and no sign of corrosion yet :-)

going to your electrics when you are not using them. worst thing ever

 I have given all my teminals a bit of glue from the heat gun. First done this 4 months ago and haven't seen any signs of corrosion or green yet. I always am wary of it too so will keep checking.  I have also heard of putting heat shrink over the glue aswell, I havent done that as I am happy with the glue so far.

 Awesome info fellas, cheers

Make sure they have used tinned copper cable for any instruments (power cables can use copper). Some cheaper builders use standard copper cable which isn't great for instrument connections.

always use marine rated cable , use a good quality crimping tool and use epoxy filled heat shrink crimps , and with all due respect to the auto sparkys out there the amount of them that still use those old style crimpers stop doing it boys it causes dramas in the long term in a marine enviroment