Im not saying theres anything wrong with doing it your way and i dont know how cold it gets where u are but im in the uk and im sure pretty much everyone who keeps em in vivs over here just go with a ceramic bulb and no under belly heating. I really dont think its a necessity although i maybe wrong (i use mats myself as i keep em in tubs in a heated room but if you just got 1 or two its pointless heating the whole room so standard practice is to ditch the heatmat and replace it with a statted ceramic bulb. Most people are able to achieve a sufficent temp gradient with just the one heat source with out any ill effects too the snake! Although perhaps if its real cold where u are its not enough for u guys idk?