This terrain was built for a local convention in January (2008). We hosted a couple space ship battle games. The first scenario required one fleet to escape from one board edge to the other while the opposing fleet had to stop them. The catch: a massive asteroid field ran down the middle of the board.
The asteroids were created by cutting out blocks of blue insulation foam and using my thumbnails to pry out chunks of the foam. If you plan on making as many as I did (50+) I would recommend using pink foam as it is less dense and maybe use a tool for the gouging to prevent a numb thumb.
The bases are actually Mage Knight figure bases. There are two styles of Mage Knight bases: the model is mounted on a small disk and the bottom "cup" snaps into that. The other base is the opposite. The base w/ the figure on it has a large window cut out of it so you can read the stat lines. The bases used here are the bottom "cups". The bases can be easily disassembled with a screwdriver.
A hole was drilled into each base to fit a length of floral wire through. The Mage Knight bases are nice because the clip on the bottom provides an easy way to make sure your holes are centered on the base. Lengths of floral wire were cut and one end was bent to an "L" shape. This allowed greater stability and glueing surface when the floral wire was pushed through the base.
The bases were spray primed black. The asteroids were given three coats of home-made textured paint. The asteroids were drybrushed from a dark grey to a white. The bases were left black because it's outer space. The asteroids were then jammed onto their base to create a hole. Then they were removed, a drop of white glue was put into the hole and they were mounted back on their base. the white glue actually adheres quite well. Do not use superglue; it melts foam!