I use magnetic bases for all my figures. It makes them easy to store and also gives strength to a relatively thin base. I use Magnetic Display's adhesive backed sheets, cover them with thin card and cut them to size. I then paint them with a rough coat of Coat d'Arms Goblin Green, making sure to paint the edges as well as the top. Then I glue the figures into place with PVA (white glue).
On a large base with lots of figures, such as these, I sometimes mount the front rank first and fill in around the backs of those figures in areas it will be hard to reach later.
I use a water based wood filler to build up the bases. In the UK the best is Ronseal Multi Purpose Natural Wood Filler. When I lived in Canada I used Lepage's wood filler.
I apply the filler thinned down with water using a combination of a tooth pick and old brush. I thin it down a bit with water to make it easier to apply. The thinner it is, the smoother the final finish. You do not want it too smooth as the final effect looks much better if the ground has a number of irregularities. In this photo the filler is still wet.
When the filler is still wet I like to press bits of lichen or other foliage into the filler along with very small pieces of gravel. When the filler dries it will hold them in place.
I let the filler dry for a day. Then I wash the entire base with Liquitex raw umber with a fairly large soft brush. I use a slightly thicker wash than I do on the figures as I actually want to stain the light coloured wood filler rather than just bringing out the details.
The reason for letting it dry so long is that otherwise the wash may cause the filler to soften and blend with the thin paint whereas what I am looking for it to delineate the details and create a sense of texture.
When the wash has dried I sometimes dry brush the raised areas using a very light sand to bring out the highlights.
Now it is time for the flock.
I apply this with dabs of white glue thinned with water. I find the final effect is often better if you use more than one flock colour. I deliberately do not attempt to cover the whole base
As these are north European troops I will use a mix of green flocking.
I will apply first a dark green by sprinkling it over the base, pressing it into the areas of glue and then shaking off any excess.
I will then apply a second lighter green static grass in the same way once the first flock has dried.
Here is the finished unit, based and ready for battle.