For regular cubensis reserve enough substrate to apply a 1/4" layer on top of the spawn/substrate mixture. It's not necessarily a casing but acts similar to one by providing an even layer of substrate the mycelium has to grow through, giving an even growth of mycelium and reducing overlay. It also helps hold in moisture. Making your substrate using the Bucket TEK you have pasturized your substrate and have it at field capacity based of the ratios I've mentioned previously. Nothing extra required for you to do and it will give you an even pin set for your cubes pluswith your monotub dialed in you won't have to mist.
For psilocybe that requires a casing layer use Jiffy Mix, it has the coir/peat, verm., and gypsum ratios you need plus pH balanced with lime. It would be nice if you ended up adding a lot of hot water to bring the Jiffy Mix to field capacity and pasteurize it like with the Bucket TEK. Unfortunately, it doesn't require a lot of water to bring to field capacity so there's no way to add enough hot water to get it to temperature and hold it long enough. That's why you have to heat it. I've seen others put it in oven proof bags (or grain bags) and place in a crock pot for the required time and temperature. There's also the old dunk the pillow case full of substrate in a pot of boiling water for 2 hours and squeeze the shyte out of to bring to field capacity by draining out the water.
For actual casing layers, you apply the casing once the mycelium has colonized the monotub 100%. You place the cased substrate into fruiting conditions, generally in a Martha tent where you can regulate humid and dry conditions several times a day. Or you can do it in a monotub by misting and then fanning a few times a day or with the setup you intend to use.
*Note the casing described above is not for PF TEK. For that you have to dunk your colonized cakes into cool water and then roll in vermiculite before placing inside a shotgun fruiting chamber (SGFC).