There is a rubber seal inside the housing but its not designed to seal that tightly. It works with normal rain fall because water wont run uphill around the aluminum housing to get to the seal area. If surrounded by ice, I could see how water would get past it. You need to get a heater up there and tarp it and melt it off or something. Could you crank the front up or down a lot to help the run off or perhaps get it high on one side?
I agree with Dakota, if storing with ice and snow on it I would double tarp it other wise it's helping to "ice dam" it and help water go in somewhere.
