By the end of today (or by the time my ears were too cold for me to stand outside any longer), I've added the rear doors and applied putty to all the outside holes. I was daydreaming while doing the doors and made some simple mistakes
But in the end they came out alright. I dropped the board on one corner and ended up cutting that corner off to make it easier to open the doors (top door, bottom right).
That wasn't the end of it though. I then attached the hinges to the wrong edge of the panel
After correcting them I was left with gaps where I'd recessed the original hinges. I fixed this by adding a strip of 'c' shaped metal to the top that I found in the dumpster. I filled the gaps with putty first.
AND, I tried to fix what I thought was an alignment problem by trimming the bottom of the top door on a bit of an angle. Once it was all installed I realised that I should have trusted my measurements instead of going by eye. I'll trim it back to square next time I work on it and if there's any more of the metal trim lying around, I'll add a strip to the top of the bottom door as well. That should fix things up.