>>509549109Problem is that those containers can take weeks to get from A to B. The extra food/water you'd have to pack in, as well as basic necessities like a toilet and ventilation would significantly reduce the number of people you can cram into a container.
Probably still cheaper than flying, but for trips between the Americas it might be better to just buy an old cruise ship and modify it so the rooms serve as cells.
I don't think there's enough oceanliners still around to do the same for transoceanic trips.