It seems to me that what's happening is salt and water are getting in through the connection there and the corroding the metal connector prong lead. The corrosion builds up and eventually breaks through the plastic to the outside and at about the same cuts the prong lead in half. I say this because a few people thought that the plastic was being attacked from the outside and I don't believe that to be the case.
So, if you can seal up the connections somehow where the plugs attach you should be good to go. For good measure it may not be a bad idea to get under there and spray water over the area to clean up external buildup. Anyone exposed to road salt should be doing this on a regular basis anyway tot he complete underside of their vehicle.
BTW, I have seen one report of a West coast truck with this problem, but I still think it's a road salt issue and more than likely this person was a skiier or such and more exposed than most to road salt. Strangely, I haven't heard of any Hawaii (just from air obviously) or Alaska trucks with this problem though.