Amazing work - you make it sound so easy.

If you don't mind I have a few questions: -
Is the canvas you use what artists would paint on or is this a different type?
Does it matter what type of flock you use? Are certain types better for this method?
Does flock continue to fall off after it dries and when it is rolled?
For your desert mat, is appears that you have used little flock. Does the sand have to be particularly fine to adhere? Did you sprinkle it just like the flock?
Regarding the large screw and washers you use to pin the mat to the table - can you camouflage these when playing?
Sorry about all the details, but this method is something I've wanted to try for a long time now.