Good for you. The Historian is right, riding at all in the rain IS a big deal.
I now have to two Balaclava, one half and one full, and I understand the fog issue. It seems that when I am riding there is no problem. It only happens when I stop. I remembered an old anti-fog trick from my SCUBA days. I cut a potato and rubbed it on my glasses and then dried them off. This has helped some. It really depends on the level of the temps though. The cooler the better. There is also an anti-fog solution that you can get at either SCUBA shops, or even eyeglass stores. Last but not least on this subject, this is kinda gross, but you can spit on your glasses and then wipe that dry and that will act as an anti-fog as well.
Good luck and just keep riding.
Jay