Fiberglass sounds shakey to me, it shrinks. It's tough stuff though
and should provide a weather barrier (if that's your goal).
I play with high voltage generators using smt parts. I can test them
without an encapsulant up to about 50 to 80 volts output. So, I screen
the boards before encasulating them. I can take the output up to 150
volts after applying 2 thin layers of clear Krylon spray paint.
After the krylon treatment, I can take the output voltages up to 300
volts, which is the limit of my components and more than twice what I
really need.
Strictly speaking, this DOES NOT protectthe edges of the board from
absorbing moisture.
But, it stands up ok over time, I have a few projects that have run
well for 10 years and still use my circa 1974 ttl keyer for my ham
radio transmitter.
Atr the time I started using Krylon, an OT (old timer) advised me I
could coat the edges of the board with peanut oil (after the krylon
layer). This prevents moisture intrusion into the edges of the board,
but I've never done this.
Lately, Krylon has become hard to find, so I am looking for an
alternative.
Regards,
Art