Have you tried GoPro's anti-fog strips, that slide into the case between the camera and sides of the case? I've been using them with pretty good luck. They are re-usable, but after a few uses, you're supposed to put them in the oven for a few minutes to really dry them out again. I'm wondering if the best anti-fog solution would be to drill a few small holes in the case and line the area around those holes with some Gore-tex material. That would keep moisture out, and allow it to breathe (and maybe eliminate the difference in inside/outside temps that lead to condensation in the first place?). Just a thought.