No mate no milking shots
I'm thinking something like this.
https://cawardenreclaim.co.uk/bespoke-new-seasoned-oak-doors-stable-divided-split-door-5273
Though that's apparently an internal door.
Trying to solve the window issue. I did a sketchup because I can't do back of ***-packet stuff like you more professional types who know what you're doing, and it helps me to understand what's going on before I do something stupid (which, given half a chance, I will).
I'm thinking (see pics) of dropping double glazed unit in front and then mitre framing it in to hold it. Security is not much of an issue in the area I'm assured, and door will be hard to access because of enclosed garden.
Someone very kindly already pointed out that you don't glue the battens, so I've been reading all round the subject!
And before anyone says, the M-I-L really didn't want clinched nails, so unless there's something terrible with woodscrewed and plugged (other than it being non-traditional) then it would probably have to be that.
Quite enjoying the challenge of getting my head around this and I'm learning a lot. Thanks so much for the generous donation of time and experience. I really appreciate it. I have limited time available at moment so I'm not fast! I know some of you would have finished it the afternoon it was requested!