The "base" textures were created using a lot of different layers at a low opacity so that they show through each other. The end result is what looks like a soft, paper-like surface. I've used it on a couple maps now and really I just play around with the settings until I get something I like. The three main components are Pattern Overlay effects using the Parchment, Washed Watercolor Paper, and Gouache light on Watercolor textures that come with Photoshop. I find layering those up and playing with the settings give me the base texture I want. I threw a few other layers in there on this map to give me the kind of color and fell that I wanted as well. I think there are a couple of "cloud" layers in there as well, again at low opacity so that they all blend together. In all about five or six layers on this map just to get the texture.
Hope this helps!
oops...reply got doubled up.