There's an easier way than that. What your talking about would be called a tray. And WBS is used as spawn, not really a bulk sub. It dries out way too easily. Depending on how much BRF you have, I would just look into a either a mini-mono or just a mono. They're a little more set and forget. Misting and fanning a little bit at the end helps, but you wouldn't have to worry about the humidity as much. And If you use coir/verm as your bulk substrate you wouldn't have to worry about a casing layer in the tray or tub. Coir performs just as good without one. And coir is pretty contaminate proof, which is great when your just starting. How much BRF do you have to use as spawn?