Gonna have to disagree with the concerns here. Fiberglass is actually way more stable than people give it credit for, especially when you use the right epoxy to seal it in place. The moisture argument falls apart when you realize how much reinforcement fiberglass adds to the hoof wall over time, it doesn't just sit there loose. If you do it right and make sure the edges are smooth, those pressure point worries are basically a nonissue. I've seen far more traditional materials like burlap or duct tape cause way bigger headaches than a clean fiberglass patch ever did. Sometimes the "wrong" material is just the one most people haven't tried yet.
Fiberglass under the pad is a wild move! That stuff can be so sharp and rigid, I'd be worried about pressure points. Seriously impressive that it worked though.
Right? It's one of those things that seems like a bad idea until it totally works. I see this all the time where people use the "wrong" material for a job and it ends up being perfect. Makes you question all the standard advice.
Actually, that method makes me pretty nervous long term. Fiberglass can splinter over time with all the movement and moisture, and those tiny shards could cause a real problem under the pad. Seen it create more issues than it fixes once the initial hold breaks down.