Step 1: The Old Train Table
I realized that the train surface pops out quite easily and has a nice frame for adding other things.
So I made a new wooden surface and painted it with acrylic paint to look like dirt and stone.
Step 2: Make the Styrofoam Hot-Wire Cutter ...
Edit: Some more notes on this ...
I picked up the nichrome wire from my local hobby shop for about $.65 per yard. The hardest part is keeping the tension on the frame since the wire stretches quite a bit when hot. You don't want it too hot where the styrofoam smokes. On the 12v setting, it drew about 1.5 amps with 1.5' of wire. Slightly higher current with a shorter length. There are other hot wire cutter instructables on this site which provide more detail on this step. If I was to go with an even shorter length of wire I'd drop down to 6 volts.
In retrospect, I should have made this frame like an X with a bungee on the bottom to keep the wire tight. But it was a hack for a quick one-off. Perhaps version 2 will be more versatile?