I have 2 Clima-Guard tubes in my box which is holding about a hundred right now. It has been touching my cigars for about 4 months now, and they are fine (they are not in cello).
In my smaller humidors (40 capacity), I have one tube in each. In order to conserve space, I attached the tube to the lid of the humidor with velcro, going horizontal along the heads of the cigars. So, it's not touching any cigars, distributes the moisture evenly, and allows me to fit an extra cigar in the box :)