I have cleaned much mold from vinyl with household bleach cut at least
50% with water. It will not bother synthetic thread, which is usually
dacron, any more than it bothers the vinyl. It will not bother cotton
thread if you rinse well (Hose it). However, I would try the oxyclean
stuff first. It will remove some molds (didn't do squat for my sails)
and seems to be more user friendly that bleach.

Ron