Funny: I've manufactured a cache container similar to this once, too, but for a very-different (and distinctly more-urban) environment (GC54F7V): seems like a bit of a strange design for a rural setting! My geo-sense spotted the hiding place right away but Robin struggled for a bit with this unusual container: he was determined to get "inside" it in some other way than the correct way, e.g. by poking, swinging, bashing, or blowing. It's my fault, really: some of the Challenge Robin ( https://danq.me/challenge-robin-2 ) puzzle boxes were pretty devious and involved exactly that kind of manipulation to get at their contents, yesterday.
Soon, I suggested the correct way to open the container and all was well. Great location; TFTC.