Most use Flexwatt heat tape for racks along with a remote probe thermostat like a Ranco.
Look at the KS classifieds under Supplies, Heating Pads, Tapes & Other Heating. You will find a number of dealers. Many of them will make the Flexwatt to your specs for your rack. Or you can buy the components and make them yourself.
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BigT
There is a difference between ignorance and stupidity. The ignorant can be taught, stupidity is beyond our control.
1.2 P. m. melanoleucus B/W N. J. Northern Pines
1.2 P. d. deppei Mexican Pines
2.2 P. l. lineaticollis Linis or Lined Pines
1.2 P. m. lodingi Black Pines
0.3 P. c. sayi red bulls
1.1 Drymarchon melenurus Blacktail Cribo
1.2 D. corais Yellowtail Cribos
1.2 M. s. cheynei Jungle Carpet
2.6 L. p. pyromelana Arizona Mt. Kings
1.1 L. g. californiae B/W Cali kings
0.0.3 M. f. flagellum Eastern Coachwhips
1.2 G. m. bottegoi Western Plated lizards