Tin boxes or ammo boxes are better than nothing, but they themselves will get very hot. The paint on the outside could then catch fire, or the heat of the metal could ignite something flammable nearby, eg. if standing on a wooden table.
Another point not mentioned is that any enclosure will reduce the dissipation of heat that batteries give off when charging, so the batteries will get warmer still which could increase the risk of failure. The pouch the video illustrated was obviously for transporting batteries - I'd be very dubious about charging them inside it. The Bunker was a great idea, as was the 'self-sanding' block pocket.
But unless you really need the performance (eg. aircraft or very fast boat use) it would seem to make sense to stay with less volatile battery types.