Hi Simon,
No, I don't recall seeing those three holes in the lower platform before. You may have seen them but notice there are at least four round drainage holes on the underside of the upper platform. U 1056 had these too.
I see what you mean about the lids on the barrel containers, this one is different to the norm. I still think it must be for a barrel due to the shape and because there was often a barrel container somewhere on the lower platform. I note that U 1305 had two containers, one on either side, I wonder what U 1308 had?
Regarding the small round holes near the waterline. These are in the position where the three elongated holes usually were. Perhaps on U 1305 and U 250 they drilled these round holes instead of cutting out the three large elongated drain holes. However, I know when I have drilled out a vent I have drilled a line of round holes around the area, popped out the part and then filed the edges of the vent with a file. The pattern of round holes on U 1305 is a bit reminiscent of this process so I wonder if a worker could possibly be halfway through a similar process?
Cheers,
Dougie