Weather proof enclosure for Raspberry Pi
One thing is worth considering and I think this is quite important. Here's the story: -

An IP69 product that was shipped to China for taking measurements of metal contaminants on a food line. It was switched-off every evening after the last shift. After about a year it failed to power up one morning. Upon opening the bottom panel (which housed the switch-mode power supply and some customer terminations), it was obvious why it had failed. There was about 1" of water slopping around.

Now bearing in mind this was IP69 rated, we immediately thought its seals had gone. No, the simple answer was that during the day, the bottom panel got warm and forced air out of the box through pressure and at night, when the unit was switched-off, the air inside the box cooled and dragged the humid air into the enclosure. After about 365 days of doing this it had accumulated enough water to reach the power supply.

Try putting a small drain and vent hose from a hole on your box to prevent this happening. Obviously it needs to be placed underneath and it needs to have a small hose from it to stop rain splashes getting in. Maybe even consider a one-way valve so positive pressure always expels.