Can I just say that heat mats aren't really suitable for cresties. They'll have to lie on the glass to get any warmth and that's not how they're adapted, they're adapted to bask in light. Heat mats only warm up the surface and are pretty useless at heating the air.
When you have the opportunity, I would get a ceramic or light emitting bulb and get a canopy (that sits on top of the tank) and use this instead (with a thermostat and digital thermometers). Cresties are know known to not thrive at room temperatures but instead do much better with basking temperatures around 30C. They are also crepuscular rather than nocturnal so benefit from UVB lights.
He's a lovely looking gecko (light ones are one of my favourites!) and seems to be in good condition