instead of teflon tape, just tried using a balloon.
I bought some 16" balloons (latex) which I am testing out for use with oil. And it occurred to me they might do a good job of filling in when the o-rings are not quite sealing.
I cut rings from the spout(?) of the balloon and slipped them around the endcaps. On the loose side (one side of my tube is slightly wider) I put 2 layers. I placed them in the tube overnight. In the morning there was actually a little bit of water inside (not enough to damage the electronics, but still, water) I took the o-rings off and noticed, on the double layered side, that the latex was not even. I cut new strips making sure they were wide enough (they narrow when stretched). I had also failed to add any grease (to the latex balloons) the first time and I added that as well. I haven't tested it again yet. I know that is a lame way to end this comment. I will post again once I have retested. :)
To be clear though, even the first test was better than I have been able to achieve with the teflon. My longest with out any humidity at all prior was 15 min. (clearly i had been doing something wrong)