Thanks for all the input guys. I decided to go with the foam boards. I created 4 separate panels, so the board size can be adjusted to fit the size of battle desired. In hindsight I should have applied a little more paint, but for a total cost of $12, I can always redo it. Here is a couple pics.
I am looking for some advice on making a new map for W@S. I have already done a large 4x8 with plywood, but I was looking for something more portable. I was considering felt or some other cloth. I am sure somebody out there has done something along those lines. Any suggestions?