I was just watching a video on underwater gliders and notice that they use a very ingenious method for sealing the end caps, which I thought was worth sharing.
Basically they use two plates, which bolt together and in doing so squeeze an oring pushing it out against the inside of the tube. You’ll see what I mean in the video. The specific part of the video is at 2:00
This method seems far more reliable than relying on the dimensional interference between the oring and tube, to generate the sealing of the oring.