You can call me skeptical!
I think most of the saving is because his freezer is
much smaller than his fridge and the fact that when you open the door the cold air does not fall out.
Now if you want to do this, the wiring doesn't need to be that complicated.
In fact I see no need to alter the freezer at all.
1- Set the freezer thermostat as low as it will go. This assures that it will always want to run.
2- Get the thermostat he recommends, I have one and use it for different uses. Even used it to experiment with Sous Vide, it worked fine.
3- Gather a power cord, an electrical box, an AC outlet, and your STC-1000.
Figure out how to wire the STC-1000 so that it energizes the AC outlet when the thermostat gets below 40*F or whatever temperature you program the STC-1000 for. Find or make a hole to run the sensor wire into the freezer and then plug the freezer into the AC outlet you installed into the electrical box.
Now if I have peaked your interest, here's a link to at least 10 Youtube videos on how to wire the STC-1000, just note: you can wire it to turn on if the temp gets to high, (for cooling) or you can wire it to turn on if the temp gets to low, (for heating).
https://www.youtube.com/results?search_query=stc-1000+temperature+controller+wiring+diagramBtw, if your freezer has a digital internal thermostat, his method will need to be followed*, but most small freezers I have seen don't have digital thermostats.
* this because the digital system needs power all the time to work. Mechanical thermostats
when set to the lowest temperature will close the contacts (unless the freezer gets to that freezing temp) so then you can externally control it by use of the STC-1000.
Just some stuff I wrote, that didn't really apply.
I have torn a freezer apart, just because I wanted to know. The insulation is just Styrofoam.
But, you have the cooling pipe on the inside and the heat releasing pipe on the outside. That is why a freezer gets hot on the outside. These two high differential temperatures are only separated by that thin Styrofoam. It would be better if the heat releasing pipe was further away from the cooling pipe.
Refrigerators can be that style, although generally the heat releasing pipe is only on the backside or they can mounted externally about 3" from the back wall. I'm sure you have all seen the pipes and with thin wires welded to them on the back of a fridge.