When you cut the coax to stuff in that tube, make sure you terminate the end to
prevent arcing at high power. Water and other things that get inside the gamma
rod will provide a path for RF to get to from the exposed center conductor to
ground. This is a bad thing. I have climbed towers in the middle of the night
during contests to fix this kind of problem. This also applies to the coax
capacitors used in some trapped tribanders.
Jim Idelson K1IR