Can't help with the silicone deterioration question, but I have a comment.
How is the water getting into the meter pan?
The pane should be relatively water tight; the conduit or cable entering the top should have a "WP" connector, and/or a hub. The head should prevent any rain from entering the conduit/cable. The "drop" drip loop should prevent water from "crawling" into the cable/conduit, or conductors.
As to the water flowing like a waterfall into the panel, I think you should seek the source.
The above is MHO, and please don't take it as sarcasim.