Well spotted for the location of the barrack block, NN. However, I must admit 'mea culpa' for calling it a barrack block in the first place. I fear the fort is so damn small, the building in question IS actually the Principia. In
you can make out the size of the Principia by the roof showing at approx 27 seconds. Also at approx 44 seconds, there's a shot of the gate from the Principia. Incidently, Lunt's granary is entirely wooden - see it in the attached photo which is the same gate viewed from outside, with the granary visible through the gate - who is that ruggedly handsome devil leaning on the palisade?
On the subject on palisade, I'd be interested in your views on the movie's pointy version. The clever Lunt people have clearly not got pointy palisade, and the movie people have it. My initial thought is that pointy palisade would be a good thing. Maybe Lunt topped theirs off for Health & Safety reasons, though I doubt it.