I had expected that it would be easy to mess the whole thing up, and that if I got the process slightly wrong the bases would look like a mess. It was, as it happened, not too much of a disaster, and I have very passable bases out of a first-time use of snow flock.
However, it could look a lot better up close, and getting the 'right look' will be difficult to attain given that there are many different ways to use this stuff.
After glueing the slate and icicles to the bases, I glued the modeling sand and painted that black with grey highlights.
When dry, I painted white the areas I was to apply the snow. This was following the Winter War painting guide, and I think is a good step, as it makes the snow stand out.
Next I mixed the snow flock with PVA glue. I am unsure of the exact ratio, I just kept playing with it until it was at a consistency where I thought it would not run, and would be opaque when dry.
Applying it to the base was the hardest part, as the mixture was difficult to manipulate.
Once it was dry, the effect was of a hard, frozen snow. However, I could see that I did not fully cover the white paint from earlier, and so rather than mix up a new batch I painted a thin, watered-down layer of PVA over all the snow bits and sprinkled some snow flock onto it. It looks bit more powdery, but overall I am quire happy with room for improvement.