Designing a humidity controller for a rack. Trying to decide between a hygrometer controlled system or just running it 15 minutes every 6 or 8 hours, will depend on season, but I'm in AZ so it's going to likely be at least every 6 hours to keep it up. Thoughts on one vs the other?

For the hygrometer controlled set-up, it would be AGPtek WH8040s for each tub, wired with diodes to a single relay for the humidifier, on the neutral side to reduce noise to the humidifier. Any tub dips below 40%, they all get a fog. I certainly don't want to have to set up an electronic valve at each tub as well, that's a bit excessive, but it's doable as well. A 1/2" valve from the garden department would get the job done for only opening the tub or tubs that are inside the trigger range. Any thoughts specific to this layout?