Also - yeah, I def wouldn't put USB BEs inside a cardboard box...
Even sitting a AC powered fan against flammable materials is a bad idea. Just ask any fire fighter.
I'm sorry if I am stating the obvious but the setup is probably a joke or an attempt to parody people that share pictures of their setup.
If not, I am sorry for offending the original poster but putting 3 BEs in a big box is an hilarious cool idea!