The tied off cord loops you have for closing the top could be a problem. My first MYOG project was a day pack that had a cord loop and cord lock for closing the top. The loop of cord caught on a parking meter while I was running to catch a bus. This resulted in me being horizontal and 4' off the ground. I wasn't hurt because I landed perfectly flat. Needless to say I was very surprised by this. People on the bus were impressed.
My pack was completely destroyed, but I am proud to report that it was the fabric that ripped, not my seams (and this was a heavy cordura).
Maybe if you untie the cord, perhaps placing a knot in the two ends, it would be OK.