I didn't have any pattern. Since the fabric was sturdy, I just used a large square to trace the rectangles with a sharpie right onto it. I started with the red canvas because that was my least favorite of the two and I would rather screw up on that one than the nice green,
I sewed the rectangles to the zipper and added top stitching as well.
Turns out the canvas is very slippery and while I usually am proud of my edging, this looks a little more like a drunken sailor was weaving across this surface.
I didn't bother lining them because they are meant to be utility pouches more than anything else. I added a little zig zag stitching on the blue and green pouch for a little extra strength.