I've been meaning to build a legit rack for my BPs, but the thermostats cost more than some of my snakes; not to discount their inherit life value of course.

I am looking to build an 8-10 high rack from PVC board and would like to use either flex-watt or seedling germination pads as UTH often get too hot for plastics and even glass in some instances (I use rheostats currently). I also worry about off-gassing from the PVC once heated.

Herpstat 1, 2, 4, etc... all seem to indicate the number of probes they support. I've seen some BHB videos and he seems to use a Herpstat 1 on a whole rack. How is he doing this? Is he/people assuming since they are all the same output wattage that they should all have equal temps? What about rising heat (thermodynamics from other sources + hot air rises) from the lower racks? Wouldn't that ultimately mean the top rack is the hottest? I'd like to build a rack 8-10 high, but want to spend as little as possible (generally a bad idea) on thermostats as they can be $200-400 a piece for multi-input. I haven't seen at 8 input but I bet it's like a $1000.

Basically, for a rack this size ... how many inputs do I really need and the appropriate spacing between racks with probes and those without? Did I miss a sticky or something somewhere too?

TIA!