Thanks for ALL the good suggestions. I decided to stay away from the "rub on" type solutions (toothpaste, soap, etc) for fear of making the bondo dust problem even worse...plus I figured that every time I wiped off the bondo dust I would also be wiping off the my fog protection. As the alternative I invested $4 in one of those 3M masks with the little exhale deal in the center. Works very well...plus the mask itself is a LOT better than the typical paper mask.
I do have to be a little more careful to keep it safe and clean while I'm not using it so that it doesn't get mashed or filled with crap like most of my paper masks do. Anyhow, the fogging problem seems to be solved...hat tip to Mikey.