How do I do containment boxes?

I keep seeing shorts of streamers getting double mirrors from their strongboxes but idk what kind of atlas they're running, what I need to roll my maps for, or if I should be doing t16s, .5s, or 17s. Can someone help guide me?

Firstly, make sure you understand that mirrors aren't just rare. These clips are fully taken out of context from a few lucky players. You could play every day for 4-8 hours for the rest of the league and not get one and it still wouldn't be even close to being unlucky.
That being said, the strat makes good currency regardless of jackpot dropps.

Scarabs:
One of each ambush scarab (basic ambush, hidden compartments, potency, containment, discernment).

Tree:
https://poeplanner.com/a/n1t

Maps:
T17s are the only option for containments. Most people run Fortress but all layouts are fine if you can handle the boss. Roll your maps for 100% combined %currency+%scarab. Packsize doesn't matter, quant is neat. Use regular chisels. Try to roll/run batches of 10 maps (or more) to get a more even feeling for the profitability.

How to run:
You click the box. That's it. Zero thought-process.

If ~2d/map investment seems like a lot I'd suggest you use the same atlas but with 3x ambush, 1x potency, 1x discernment on T16.5s (or 8mod T16s) first to get a feeling for the strategy since that version is a lot cheaper but still very solid.

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Most people run Fortress but all layouts are fine if you can handle the boss.

And if I can't kill the boss? I'm playing VFoS and its boss dps is in the bin. I thought 100m dps would be good for a boss but I think my skills end up killing me and I can't down any t17 boss easily.

Not being able to kill the boss is an issue that you have to solve. Personally I simply wouldn't bother running T17s at all if I can't kill the boss because losing out on 40-600c (fragments, Yoke) on every map is really bad and instead I'd just go with the cheaper variant on T16.5s.

You have 100m on vfos and can't kill the boss?? I'm confused because my pob is showing 4mil and I've done every boss all fine besides Ubers..and even the streamers build guide I kinda followed went crit/enmity embrace and is only 4.9mil