You can spread them out in the sun on a nice dry day; the light and heat will dry out and kill the mold (Turn the frames over after a while). Then when you put the supers on hives, bees will finish the clean up, though if the comb is pretty wooly with mold you may try brushing them off before putting on the hives. I wouldn't put plastic around stored supers, but you've already probably decided that change for next year.