I would say no, for fire hazard reasons....you don't want a CHE near a plastic tub.
When you have a tub and a 70 degree room you need to do two things....heat the room to your required ambient temperature of 78-80 degrees with a radiant oil heater, AND then you need to provide your hotspot via an under tank heater (either a uth or heat mat) for the tub on a thermostat.
A PVC cage of your choice, a radiant heat panel, and a thermostat are really the most economical way of caring for a boa if you want an animal without health problems and you don't heat your entire room to begin with.