[TowerTalk] How to waterproof a split coax feed to yagi?

[trappaport at austin.rr.com]

To feed my Force 12 HF yagis, I plan to wind my own coax baluns (8 turns of coax, 8" diameter - sound reasonable?), and would like to simply spilt the LMR400 coax feedline, with the ground braid going to one side of the dipole element, and the center conductor to the other. 

I am wondering what is the best way to **waterproof** the split coax. Is there some type of goop or sealant that has excellent waterproofing and UV resistance, that I can use to keep water from seeping into the coax? I would welcome any thoughts and sources....neither Home Depot or Lowes had anything that seemed like it would work.
73 and thanks. Ted N9NB (trappaport at austin.rr.com)