ceramic heat emitter running 24/7 with a thermostat whos probe is in it's cool zone.
Solid timber lid to keep heat in the viv.
You can use a heat mat sandwiched between two layers of tiles ie
https://www.beardeddragon.org/forums/vi ... 5&t=224976 , works a treat for my BT skinks and beardies , all 4 love their nice warm beds , and my water skink loved her's too. I don't need more than a 7W heat pad for each of my gang because it NEVER gets freezing cold here ( 3 km from the Pacific in northern NSW Australia (33 deg S lat) , rarely colder than 10 degrees C here overnight.