What they forget to tell you is that you would need to fit it very precisely, then test it. Then you would have to work out how to get any services (water, electricity) into it without cutting a hole big enough to cause a leak. You would also have to find a way to isolate the mains electricity so that any emanations from within the room are not detectable on cabling outside the room. Otherwise you wouldn't have an actual
NSA-grade TEMPEST setup (as hinted at in the linked article) just something you hope works well enough.
