There are a few ways to heat your boas' enclosures. In a cool room, a radiant heat panel is the best option, IMO. In a warm room, above 75 F, heat tape is a better option. You would tape the heat tape to the bottom of the cage one side, using foil tape. The tape should only be taped to 1/3 the length of the cage. I use 12" heat tape for my cages. The tape must be hooked up to a thermostat. I suggest a digital thermostat, such as a Helix, Herpstat, Johnson Controls, or a Ranco. You should also purchase a temperature gun to measure the hot spot to ensure that it does not get above 92 F.
An overfed boa may have many issues. The worst is death. Jeff Ronne from The Boaphile said in one of his videos that early in his career he had some deaths due to overfeeding some of his boas. Another issue is them not breeding due to being overweight and unhealthy. Boas do not metabolize their food as fast as some other snakes, so need to be feed less often. They also eat larger meals than some other snakes, which will take longer to digest. A good feeding regimen for common BCIs is once every week until they are approximately 1 to 1.5 years old, then once every two weeks until they are around 2.5 to 3 years old, then once every three weeks. By this time, they will likely be on extra large rats. Eventually you may even be able to feed them a rabbit once every four weeks, if you prefer.
I hope this helps.