Swim puts a circulating fan near them so there is air exchange. He doesnt use perlite, there is no need since the sub makes it own moisture. He just lays down a trash bag (mainly so he can lift out the colonized sub to dunk them) and lays a layer of colonized grain/sub/small grain layer then a small sub layer on top of the grain. Swim would have to say 3-5 inch sub depending on the size of the tub. Swiy can case the top part of the sub but there have been reports that there is not much of a difference in casing if you use a sub already high in the proper nutes. Swim recommends straw/manure or coco coir/spent coffee grounds/verm/manure. Swim didnt case this tub.