And getting back to the original subject---
Out of curiosity I have conducted a non-scientific test, and JB weld seems to be a very good thermal adhesive!
I took a small chunk of scrap aluminum, placed a 6V incandescent flashlight bulb at one end, and a temperature sensor at the other end. To keep the bulb from directly affecting the temp sensor, I wrapped it with a piece of foam. I then turned on the light and watched the sensor reading go up as the temperature rose.
I then formed a chunk of JB weld about the same size and shape as the scrap aluminum chunk, and repeated the test.
The results were nearly identical. If anything, the JB weld seemed to conduct the heat faster than the aluminum!
The JB weld is semi-conductive, so that needs to be considered with any potential design.
And JB weld is available almost everywhere and considerably cheaper than commercial 'thermal adhesives'.