My racks come with heat pre-installed. Either heat cable or Flexwatt. The heat cable is routed along the rear of the shelves, across the bottom, down the side, across the bottom, down the other side. The Flexwatt goes straight down the back wall of the rack.
All racks have a Herpstat ND thermostat and probed digital thermometers.
I use Animal Plastics Economy Plastic 66 quart racks for adults and Reptile Basics 16 bin Iris hatchling racks for hatchlings. AP has the heat cable (special order, they usually use Flexwatt) and the RB racks have Flexwatt.