The only working tip is building a roof (transparent)so that the rain dont reaches the flowers. thats the only practicable thing. before flowering rhe rain doe not do any harm. and yes its strain related . the denser the plant grows the higher is the risk of moldering. Most time i have to harvest 4 weeks before the end of dlower because of the rain that takes days. The only thing that helped me buiding a roof against direct rain. happy growing