I'm pretty sure every outdoor rated cover comes with either a gasket and or 3r style drain. The gasket should keep water out if the outside building envelope is sound.
My area has a high humidity most of the year and that along with nobody ever seals even a flush mounted box that causing air to flow thru and cause condensation. Years ago I started to use fiberglass wall cases on all boxes that supplied not only outdoor luminares & receptacles but on interior walls that were on inside of exterior walls. Used bathroom silicone caulk ( not suppose to mildew ) to seal cable entrance and finished edge where box meets sheetrock .
In the Southwest there are very many (probably millions) of residential breaker panels located outside, with the NM for the branch circuits running directly to the panel.
It's been this way here forever. I agree it would be better inside but it really hasn't been an issue in our climate. GFCIs seem to last fine. AFCIs don't work regardless.
With all the heat and sure bugs & spiders in outdoor panels any guess on how long the average say 15 & 20 amp single & two pole plug in circuit breakers last?. In my area we have over 60 year old panels with all the original breakers still operating. They are in basements that are heated and most likely never in a temperature below 60 degrees or hotter then 90 degrees. In my 60 year old development they installed ITE Pushmatic panels and had done free work in at least a dozen of my neighbors homes and only had to replace a 30 amp two pole breaker for a central AC unit. Always keep some in stock for this. Of course neighbor cried when he paid thru the nose at local box store for that Pushmatic breaker that I asked him to replace for the one that I installed during a heat wave.
