How to install thermostat with plug in heater?
The controlled AC outlet you linked to in the comment above seems like overkill unless you were intending to run all of them from one thermostat.  I'd actually recommend putting all of them on individual thermostats so you can keep them in 3 different heating zones.  Not only would this be much cheaper (the relays don't even include the thermostat), but it would be a "plug and play" solution without having to wire all of the signal wires back to the relay.  I'd take a look at something like these.