I saw this idea on someone's blog ages back, so if it was you - thanks.
As we all know, it is annoying playing a game with nice terrain where you have to keep fixing up trees as they fall over. One solution is to make larger bases as forest templates with fixed trees, but then it can get awkward trying to move troops around the fixed trees.
Another solution is to base trees on individual, magnetised bases, then make a template from a sheet of steel.
First up, find some galvanised iron sheeting or similar and use tin snips to cut out the shape of your forest.
Then brush the sheet of galvanised iron with PVA glue, and lay sheets of toilet paper or tissue paper over it, wrapping some around the edges. The first time I tried this I made some diluted PVA and dunked tissue paper in it before trying to put the paper on the steel. Don't do this - you end up with big clumps everywhere.
Once you have done this, and the PVA is still wet, mix up some more PVA with water and use a brush to carefully go over the tissue paper. This will ensure that the paper ends up well glued to the steel, but it also gives texture to the paper. Note the all-important beer.
Finally, when your forest template is dry, paint it brown, drybrush your textured highlights and add clumps of flock as you so desire. You now have the outline of a forest. If you base trees on individual magnetic bases you will have a forest that doesn't keep falling over.
Now the real challenge is to try to cover terrain features like hills with something that magnets will adhere to. I have thought about steel foil (which I haven't been able to find in Australia), ferrous paint (very expensive) and even using steel filings as flock under a coating of PVA! Anyone got any ideas?