I am rather in the same boat with this one, has everyone had a secret longing to do the Winter War?
The only winter terrain I ever made were a couple of stands of conifers, as a test one was winterised with white textured paint and the other with marble dust. The textured paint won on all counts being easier to get, easier and quicker to apply and looked much better and not looking like something you could be arrested for possession of.
There was an article in Wargames Illustrated many years ago that suggested using melted candle wax to do frozen water. At the time it seemed a great idea now I am not so sure.