Got my lash up finished, haven’t posted the pics yet.
Turned out pretty simple actually. Pulled the switched neutral from the power switch and tied them together. Put the power for the 24VDC supply on the now vacant side of the switch. That was the easy part.
Added two temp controlled relays. First one powers up the 24VDC supply and provides input power to the heater. The second one takes the power from the first, and energizes the heater when the actual coolant temp falls even further.
The aquarium heater slid right in with a stabilizing rod once I removed the extension tube.
