40C is 15F to hot. its 104. You should be at 88-92+/- So that needs to drop quit a bit.
Your best bet is to get a overhead lamp, and a CHE or Red heat bulb and adjust it to height to offer his correct hot spot. Do not get a heat pad unless you get a thermostat with it. With Temp fluctuations a Rheostat will not work as it will go up/down with ambient heat drops/raises.