Despite mounting the 6V regulator (which feeds the valve heaters) on the rear aluminium panel, I felt it was still getting a little hotter than I would like so I mounted a finned heat-sink to the panel and that seems to help the cooling quite a bit. If you are going to do this, make sure you remove the area of the vinyl label under the heat-sink to improve the thermal conduction.
After running the unit for an extended period I was also worried about the temperature of the Arduino Uno’s on-board regulator. Arduino recommend an input voltage of 7-12V but the unregulated 12V from ecca’s board was more like 14.5V. I therefore have fitted a separate 9V regulator to supply the Arduino and it is now running much cooler 🙂