I'vde started switching my stacks over to multiple thermostats. Too much gradient to control the whole stack from a single point. The upper tubs are warmer than the lower ones. For my large Iris CB110 tub rack I've gone to a Herpstat PRO 4 channel stat for each rack. Have divided the rack into "zones" into 2,3,3,2 tubs each. Another HUGE advantage for me is I keep both BRB's and BCI's and can now keep them in the same racks.
(note, older pic still with one herpstat per rack)

For my smaller tub rack, I've gone to two helix units for each. OK, only have switched one over so far but do have the stat ready for the second rack. split into 5 shelves per stat.

I like to put the stat probe right on the heat tape. Then I set the stat low and adjust up until I get the temps I want in the tubs.
I use heat tape, under the tubs. One row per level, individually wired so I could turn off a row if not in use. Just tape it down securely. Oh yeah, I did route a shallow wide groove to set it into.
Don't know much about heat cable....
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Thanks,
Dave Colling

www.rainbows-r-us-reptiles.com
0.1 Wife (WC and still very fiesty)
0.2 kids (CBB, a big part of our selective breeding program)
LOL, to many snakes to list, last count:
21.29 BRB
19.19 BCI
And those are only the breeders 
lots.lots.lots feeder mice and rats 

