For my 2 different boa cages, I use 2 differnt methods of heating. I'll say the pros and cons of them

For my 4' by 2' cage, I use a 150 watt red bulb. The pro is great night time viewing. The con is Harder to keep humidity up

For the 18 qt tub I keep the other boa in, I have an uth under 1 half of the tub. I hate the fact that you have to turn on the room lights to see the boa but its easier to mantain humidity and temps at the same time

Its really up to you