BOOTY MONSTER,
Fiberglass deteriorates if exposed to weather, a lot like wood. To preserve wood, or fiberglass, when so exposed, you usually coat/paint them with something that's sort of weather proof (and in the case of an antenna, non-conductive). And metal stuff too, as far as that goes. Wouldn't hurt to take down a metal antenna periodically, clean the corrosion/oxidation from the joints, reassemble, then put everything back like it was.
Nothing lasts forever. Some things tend to last longer than others. Fiberglass tends not to be one of those longer lasting thingys without maintenance.
I tend to shy away from fiberglass if I can. Fiberglass antennas work just dandy, but they don't like me very much, make me itch/burn/cuss a lot.
- 'Doc