Where do you put temp/humidity probes in a rack?

Hi all!
The boyf and I are talking again about the possibility of taking up snake breeding to sell one day, and we'd want to get a rack. Now, this isn't going to happen any time soon, but I still want to do as much research as I can :D
One thing that I'm confused about is temp and humidity probes in the rack. We're going to use heat strips (Not sure if they're called the same in america, I guess it's the same as heat tape?) across the back of the shelves to create a gradient going forwards. Each shelf will have 2-3 tubs depending on size. So, what I'm wondering is that since they're all on the same heat mat, would I need one temp probe per row or would I need one per tub? Because surely it would be the same-ish at all points of the row? I don't know :D And also for humidity, do I need one per box? I think I would do in case one of the babies spills their water so I'd know the humidity was too high at a glance.
Thank you all in advance :)

Generally what is done, is one probe for one thermostat. So an entire rack can be run based on the reading of one probe as long as all the heat tape is the same size and you have not exceeded the limits of the thermostat. There will be slight temp variations between tubs and you make adjustments on the whole thing from actual readings from a temp gun.

This is of course a little bit of an over simplification. Many people will run a backup thermostat inline in case the first one fails. I personally got sick of all the wires and heat tape and just heat the whole room.

Ah, thank you! That makes sense :)

I tried one probe for my whole 7 foot rack but I found that the temps were all over the place, so I bought the four probe thermostat units and run two of those plus another one, so seven probes for seven levels. I know it's a bit extreme but all my levels are dialed in exactly where I want them to be. The good thing is that if I keep different kind of snakes or decide to breed just one level I can change the temps for just those particular snakes. I also put separate temp alarms on all my levels just in case, the biggest thing being if one of my thermostats were to come unplugged, the levels would get cold and there would be no way to know.

I struggled with the temp probe placement too, but I just use duct tape and tape it directly to the heat mat right between the tubs. For some of my probes they come with a probe holder with sticky tape on one side, basically does the same thing, just holds the probe in place with a small piece of plastic. As long as my heat tape is at the right temp I don't really worry about tub / substrate temps. If the snake digs down in the substrate to sit on the bottom of the tub they get close to the right temp. I'd rather be a bit cooler than risk overheating my snakes. I also keep the room between 79F and 81F.