It's flex watt heat tape. They run it across the back/bottom of each shelf with a hole in the top back of the rack for your thermostat probe. Which is then taped to the flexwatt.
Ventilation?? Most of us don't even put holes in our tubs. The gaps between the top of the tub and the shelf are enough. For smaller tubs, a few holes can be put in the front of the tub to prevent condensation build up. That's plenty of ventilation.
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