My goal was to build a two part mold using the vacuum former.  My strategy was to vacuum form each half using some cardboard to offset the vacuumed form.

Here is the second pass where I include the cutout of the vacuumed form from the first pass:

And then things started to go awry....  I used the urethane rubber with 40 hardness.  I ran into a few issues.  First, I should have used mold release.  Also, my two part mold leaked a bit, and I think there was something wrong with the urethane.  Even after 48 hours the material was still quite tacky.

Here is the two part mold stapled and taped together:

The part looks pretty close to the chess piece.  Unfortunately the material doesn't lend itself to cutting the flanges and sprue.  

I also soldered some leads onto an LED to use with the gogo board and the arduino board.  I found that adding some solder to the ends of the wire helped to make the wires manageable with the board headers.

Here is a video of the LED lighting up as the magnet embedded in the chess piece approaches a magnetic sensor:

Video