There's always moisture inside the trap when I disassemble the thing,
so I'm wondering if maybe I shouldn't be trying to tape up the traps
at all - maybe they are retaining water or something that is affecting
the capacitance. Each trap has a drain hole at the bottom, and the
aliminium pole itself has drain holes every now and then that I'm
trying not to interfere with.


It's very difficult to hermetically seal a large surface-area container from
moisture ingress. What happens is that, on a warm sunny day the container
heats up, causing the inside air to expand , pressurize the container
somewhat, and leak out. Then a thunderstorm blows in and cools the container
suddenly , causing the inside air to quickly contract, pulling a vacuum and
consequently sucking in some of the humid outside air. The humid air that
was sucked in then condenses back to water, which remains trapped unless
some reasonable size 'weep' holes are provided at the lowest point.

The moral of the lecture is that, unless you have taken substantial measures
to guarantee a hermetic seal, you should have drain holes.

Joe
W3JDR