Here we have a stout wooden box with just a small hole in the front door.
You brought your pencil right????
With a pencil in hand it can be inserted into the hole which will disengage the internal lock and allow the door to open, no problem.
A suitable waterproof box, log book and pencil will be supplied along with woodscrews to attach to a post etc.
Youtube Clip - https://youtu.be/o8vFobsA0Og