Most people that have tub set ups or racks use 3 inch flex watt heater tape, you can purchase it from Bean Farm, LLL Reptiles or Big Apple. You will also need a proportional thermostat, helix makes a good one so does herp stat from robotics.
If you have more questions feel free to call me at 408-981-6694
Good luck
Brian Gundy / For Goodness Snakes