Re: Securing canvas mats. (Update)
Tested the securing system described above and it seems to work really well. There is a tendency for one of the board to lift a little, but I think I can fix that by restringing the 2x4 in the opposite direction that I have it now. Might try also try applying left over scraps of velcro to the 2" side that faces the mat to provide a little extra grip.
I am so glad this worked. I need to make about 10 more, and that's only going to cost $60.00 ($72.00 for 12 total sets). Not to shabby for a portable, reliable, and adjustable framework for 1200sqft of space.