Reply to "Does anyone know how to model a side of the road snowbank?"

I might add that I have used foam to make boulders (not snow banks) and then painted them.  The problem is that I had to glue them down because, unlike Plaster of Paris, there was no weight to them, being made from foam.  If you do decide to use foam, make sure it has a flat bottom.  If your train goes by and it's not glued down, you might experience a flying snow bank.