H- glass for SUP?

Nope.

It’s easy to realize that there is no reason to have stronger glue joins than the strength of the foam (10kg/m3 is pretty weak).

Next thing to realize is that the foam’s function is purely to support the deck and bottom (keep the distance between them constant). From here you can see that there is structurally no glue needed at all! (assuming that you’re only glueing pieces together horizontally)

However you need the pieces to stay together while shaping.

But 10kg/m3 is too weak to support a thin laminate, it dents to easily. But it’s perfect in supporting a 3-5mm sandwich skin.