This is a "pet project" of mine (pun intended) dating back a couple of years. Gary's page was my inspiration, since he was already experimenting with these. After I had a go at it, Gary has improved the insulated box design several times over, and it shows in the efficiency data he's collected.
Where I live I need electric heat (usually) between December and March. The insulated stock troughs have reduced my electricity use drastically. I have also started employing the water heater in the stock trough as an "auxiliary" wind turbine dump. Not official yet, but this extra step is close to providing the majority of the water thawing electricity from my wind and solar equipment.
How did you notice this subject? Aren't you sweating these days?