I hear about how I should have a humidifier gadget for my guitar and again when I bought my ukulele. First, is that true? Guess it depends on where you live, like the desert or myself in Colorado at 9000 ft. The other part of the question is, does the humidity or lack there of affect your cigar box?
Back when I was reading Guitar Player magazine monthly, some luthiers did recommend using a humidifier if you lived in a very dry climate. Depending on the construction of the instrument, cracks could develop over time.
However, cigar boxes are not constructed like guitars, which have lots of curvy surfaces and thus uneven pressures and tensions. Everything is in pretty much a straight line.
Still, these boxes are not made to last forever, after all. If you have a good solid-wood box, and live in a dry climate, it's probably not a bad idea.