My suggestion is this. Since leos are nocturnal, they don't require uv light but it won't hurt them either. I would get a low watt compact UV coil bulb, they are about $10. They will fit right into your dome lamp. They don't put off heat, at least not nearly enough to warm the tank. That way you can give your leo a day /night cycle, some benificial (not required) uv rays to bask in if he likes, in the dark room.

Then just use the UTH as a primary heat source since they need belly heat. Just do 12 hours of light, 12 hours of no light.