While you're in veg, run the exhaust fan on low and let it settle in to show you what kind of heat and humidity the tent will retain with the light on. Put the heater wherever (in tent etc.) and let it acclimate to the temps. Turn the heater on and bring up the temp until you hear it kick on. That should roughly let you manage the swing as you're trying to set the heater to turn on when the temps drop a degree. If you need the daytime temps to be higher than what you're light and slower circulation can give you you'll need to bring up the heater to put you near your daytime target temps and let it turn itself on and off to keep it there. Once the light goes off the heater will likely stay on a lot longer but still help you keep the swing down.
If you get to a point where you're happy with it all start trying to dial in VPD and you'll be playing in the big leagues :)