I had an experience after launching a 742or1-f with one GEN on MEL in the rain. Had an ATB after being about an hour out (not sure, does not matter). Anyways rain water had fried 2 more GCU's (3 GEN's out) and the 741/2 made it home with out event. The scary thing was how easy it was for rain water to make it to this rack in the lower 41. It is not far from the main entry door.