I decided the two winter panzers needed some snow on the bases, so this is how I did it.
The bases were prepared in the usual manner: sand (normal beach sand) glued onto a balsa wood base, with magnasheet stuck underneath, and sprayed black. After that, I sprayed a thin layer of white paint at an oblique angle from all sides, to give the sand a bit of a dusting of white - faster than spray painting.
I originally wanted to stop at this point, to keep the bases simple. You can see what this stage looks like in the earlier post on the winter panzers. I thought there was something missing though, so I decided to try and put some snow on the bases.
Options included using white glue mixed with white paint (since white glue sets clear), and putty wall filler. The first would've resulted in smooth globs, which I didn't quite want, and the second is a bit harder to control (though I thought it might give the effect of packed snow quite well).
In the end, I settled on the modelling snow I bought some time back. This is a specialised flock, made from some sort of plastic. It looks white, but is actually semi-transparent (as I found out the first time I tried to use it some years ago), so I mixed up equal parts of white glue, water and white paint, and then stirred in the snow until I got a putty like consistency, which was then slopped onto the bases.
The white paint counters the transparency of the flock, and the glue globs it together. I opted not to cover the base entirely, aiming for a spring thaw look to the whole thing (extending my options: this way, the models won't be limited to only deep winter scenarios, but could possibly be used up to early spring).
In retrospect, I might want to try the putty filler for the next time I do this - it might make a better basing material for deep snow.