This is basically the same thing — but outdoors.
You can make a soil factory in any type of container, or directly in a bed of pallet collars or some other kind of frame.
The difference is that you will have rain and snow to deal with if it is not under cover, and that you can have a much bigger volume in your soil factory if it doesn’t have to be moved.
Drainage is the first thing.
If I’m using a tub or barrel I either put in a layer of charcoal or other absorbent material if the soil factory is under a roof, it’s not that different to an indoor soil factory from that respect.
If it’s going to be out in the rain and has no natural drainage, I tend to drill a hole part way up the side so the bottom of the container forms a reservoir. I fill up to the level of the hole with drainage material — leca balls, ceramic scraps or charcoal. Any runoff over this level will drain out through the hole, but up until that point it will be stored in the soil factory and hopefully soaked back up into the soil by osmosis.
The other option is to build a box from planks, or pallet collars, or some other form of barrier. In this you can make soil on a more or less permanent basis, just keep digging down your bokashi buckets when they’re ready, and dig up the ready soil when it’s ready.
Depending on how strong you make the mix, this soil from your soil factory can be used as fertilizer if it’s strong, or a lightweight mulch if it’s weaker. Or for filling planting containers or transferring to other garden projects.
If you keep filling the same soil factory with bokashi, and removing soil from it on a regular basis, you’ll end up with a really fast production process. This is because the remaining soil will be really alive with bokashi microbes, and these will kick in and speed up the process every time you add a new bucket.
Your soil factory will, however, eventually get really strong if you keep adding bucket after bucket of bokashi.
You can balance this by adding some new soil: clay, sand or peat depending on what you have available.
I sometimes choose to ”dilute” my big outdoor soil factory with filler materials. A pile of newspapers scattered across it, a heap of saw dust (chemical-free), a load of wood chips or other woody garden waste. None of these materials add any great level of nutrition, the whole point is actually that they shouldn’t, but they do add structure and help to lower the nutrient level.
Generally, I tend to avoid using my soil factory as a garden compost, although it can be really practical to dig down a pile of green garden waste sometimes. There’s no hard rules about this, just do whatever works best for you.
But do watch out for weeds and potentially active roots and stalks. These will most likely be encouraged by the EM/bokashi environment and grow even stronger and better than they would have otherwise.