Because nobody has your setup. Nobody has your room temperature exactly, nobody has your air pressure, nobody has the exact same room insulation. I mean, if I told you that the rack would NOT heat up enough with heat tape down the back, and you decided to put it on each shelf and you lived in Arizona, bad things would happen. If you cooked all your BP's because of my advice, you'd want to come kill me, nes pas?
Moral: Heat tape down the back works in some cases (most actually) and heat tape down the back doesn't work in some cases (rare). That's the whole point about having quality thermostats, quality cage design, and a good, isolated/insulated reptile room. Its also why EVERY SINGLE REPTILE BOOK tells you to set up your cages well in advance and monitor the temperature gradients 2 weeks BEFORE you put a snake in them. Point is, don't worry how everyone else does it. The temperature gradient numbers are everywhere out there (90-92F hot spot --- 80-85F cool end) so just build something that acheives that in YOUR situation.
Makes sense, don't you think?
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