I camp with kids so of course I have experienced zipper failure.... In all my tents sooner or later. They blow through the doors without fully unzipping them, snag a foot, and pow, good bye zipper.
My local SoCal REI had an arrangement with a "little old lady in Pasadena" (say it with me: 409, 409....), who would replace your zippers with MEGA zippers. For about $100 she'd lace in a zipper that could be used on the face of the Hoover Dam. Money well spent.
Not trying to hijack BUT where can I find more about these MEGA zippers??? A Google search comes up with a lot of info on MEGA zipper. Ironically non of it is about a zipper.
Darrell