Not Doc but the Supertarp annex actually only attaches at the top to the pole and at the bottom by the stakes and depends on overlap of the tarp itself. I wasn't too thrilled when I set mine up and figured I'd be adding some velcro at some point. However in its original form it has held up to some major alpine rainstorms. No wet despite lots of wind and rain in my case. I still may add some velcro at some point just because I have the same concerns as you but as of yet they haven't been born out.
