Here’s something else I’d forgotten I’d worked on before C4 and not posted.
The original dome periscope had a small raised lip around the side ports/windows. Neither my PVC or aluminum periscope kit has this so I improvised.
I used a 1″ Nylon gasket from the plumbing department at my local Ace Hardware store, and just superglued it in place. However, paint has a real hard time adhering to Nylon, so if I was to do this again I’d probably try and find an O ring made from something different. Also if you try and rough up it up you’ll get fine strands that will never go away.
I guess I’m posting this as an idea rather than a solution.