30yrs ago I had many runs of Belden 9913, which is a hollow and mostly air dialectic coax. I would consider myself a professional antenna installer having worked in the business most of my life and I tend to over do most of my installations having seen what happens if you don't
With that said, all of my 9913 coax runs failed after about 5yrs with water I could pour out of the coax. One end of the coax was indoors and the other was shielded from rain and well waterproofed, leaving only a possible transfer of atmosphere from the outside to the inside of the coax with temperature changes and condensation happening inside the coax. The same thing has happened to most people I know using 9913. Bottom line is, don't use 9913 and go with a closed foam dialectric coax like LMR400 instead.
I have many runs of LMR400 and LMR500 at home with the oldest being about 15yrs old, and it still looks new if I wipe off the dust. It should last 20-30yrs no problem outdoors.
I've taken apart some Andrew Heliax runs that were a good 30yrs old and installed per Andrew specs with Andrew monkey goop over Scotch brand tape and the connections looked bright and shiny like new. If properly installed, Heliax will outlive the installer and then some.
prcguy