I'm just curious about something here... If we're all talking about just a standard NEMA 3R panel outside... we're not talking about a gasketed, and sealed enclosure. It has a deadfront that allows airflow, just as much as the flop-down outside cover would. I don't see how any condensation that might accumulate wouldn't just drip out the front of the panel, just as easy as it would a "weephole". I've used the tiny knockout in the bottom of most every panelchange I've performed, in many different jurisdictions in California (and one in NY), I've never been shot down or even had this brought up as a weep hole.
On a semi-flush installation, I'd think it would be beneficial for any mishappened moisture to make it's way out the front, rather than ending up inside a wall where all kinds of fun stuff can happen.. (toxic mold caused by an EC would be a lawyers heyday! [Linked Image] )