Can you store the stuff after it's mixed? I'll probably be using it to apply mud to the running gear of tanks and such and I was wondering if I could bix up a batch and store it in the freezer or an airtight container for when I need it.

I never had much luck storing it. You may try tupperware in the frig. I kept some in a zip lock bag on the bench once and it sprouted amazing amounts of blue fur, quickly...