Hi Don and Mark.
As mention many times before, the museum U 995 do not show the real U 995 and I can not remember the markings in question. I checked with the limited documentation I currently have access to and I guess the markings are related to the alteration to the hull, making the museums version. The markings were not on the hull at the arrival Kiel from Norway, the first time I noticed the markings was when the hull was placed on its concrete bed at Laboe and having access doors for the visitors. As to the Kingstons for MBT3 they are indeed rectangular, but welded shut for security reasons, as the fore free flood gates in the casing. It is possible to crawl into MBT 3 through the Kingstons, I have done it myself, and to climb on the casing side using the free flood gates as step holes ( which I have not done). My image below shows the story.
Tore