With 3 sides of the oven now insulated by "fire blanket" material and aluminium sheet, it was time to make another temperature curve. This was also a literal "smoke test" to make sure I hadn't broken anything while fitting the insulation and the power socket.

There was actually a little bit of smoke but it went away after a few minutes. Probably just some fingerprints or a bit of dirt cooking off the surfaces. Now let's have a look at the temperatures:

The insulated oven is shown in red. You can see that I got a bit lazy and shortened the test period.  The temperature seems less stable than the uninsulated oven, but these tests were performed using the oven's stock temperature controller, which will be replaced with a K-type thermocouple (or two!) and PID control of the heating elements. The important detail here is that the oven heats up much faster. The insulated oven got to 200 degrees in three minutes, while the stock oven needed almost five minutes to get to the same temperature.

I can possibly improve the performance a bit more by adding some insulation batts between the outer enclosure of the oven and the inner walls, or perhaps by improving the seal where the door meets the body of the oven... but the performance at present is much improved, and I consider it to have been worth the hassle of almost completely dismantling the oven! Any further tweaks can be made without having to do a complete teardown of the oven, and can therefore be postponed indefinitely.