Cover with cardboard, poke holes in it first , that'll keep the moisture from escaping. Cover with a bag too if the cardboard doesn't do a great job, but I think it'll be enough. Mushrooms work best with very low light so even if the bag is opaque , or milky it'll still grow. . Hope this helps. Just to prevent any possible spore contamination in the house, those things travel. It really isn't worth the risk. They get into clothes damp clothes or spots of your house you never.knew was damp.