Fiberglass insulation that doesn't stay wet or attract mice?

Based on a little googling, it looks like the encapsulated batts are not really moisture-proof -- they have a moisture retardant barrier.

But that gives me an idea -- what about stuffing fiberglass batts into heavy-duty bags, sealing the bags, and then stuffing the bags into the empty spaces around the tank?

If properly sealed (a big if), the bags would completely exclude all moisture and would protect the fiberglass.

The fact that I have never heard of this technique makes me doubt that it would work . . . .