mildew but not the stain left for a long period i have used pure bleach on some . as far as armoall it is just a sunblocker and a petroliam product thet will make the vinyal stiff . vnyal bed cover mfg. will void warenty if you use armoall on it .dry them off after they git wet or cover them with a cover that can breath or vent the boat so it will not sweat.