Could you compromise with your set up? For example, if you traded from what you have (not sure if he's in a tank or tub...) to a flatter tub, you could use 2 heat mats on a thermostat to maybe achieve more sustainable heat. Also, even the larger-sized under tank heaters seem to list a 24 watt use out of the box, and you would have to use a thermostat to regulate them which would mean less than 24 watt consumption. The tub would hold your ambient better even before insulating measures and if you had over-sized regulated heat pads covering the majority of the floor of the tub you can get pretty exact with the temps you want throughout your enclosure and still come up using less than the 75 watt bulb that's not quite cutting it.