The way I might to stippling is to create a smaller image and hand stipple it and then keep that on file. Then when you come to a map just draw with the tablet the mask area and create a repeating version of the stipple and mask it into the main image. Sometimes you can see the repeat lines but if that is the case then mask in several versions of the stipple at different sized repeats. You might be able to get the PC to create some stippling for you with random noise too. So your only job is to draw the shape of where you want it.