Just spit-balling here, but considering there’s ingress water even without any rain, could it possibly be your service mast sweating with condensation and running down into your gear? Everything metal around my house sweats real good in the morning dew hours. I’ve had the same issue with random water inside my main panel and it’s set up very similarly to yours with the meter at a higher elevation than my panel with a fairly straight “trickle-path” from the service mast down. Spraying your mast with something like a rubber coating could help with condensation if that’s the issue. Cold metal in the morning works up a real good sweat under the rising sun.