I use a Herpstat Pro. Which has 4 probes. Its 4 proportional thermostats in 1.

For the RHP's they both get theyre own probe. Then the hot side flexwatt is wired so both cages have just 1 plug (parallel). Same as the cool side.

And then i just put the other 2 probes on one of the cages. It controls that piece of flexwatt. And since its wired into the other, it heats that one up too.

Most times the RHP is fine stand alone. I just keep the flexwatt on the bottom of the cages to keep it from getting too cool. Just for peace of mind. They hardly ever turn on.