Comment by Lio
I wonder, how hard would it be to make a vacuum insulated oven like a big thermos flask?
I know this is “low-tech” but still think it might be possible to fabricate something even if it means spending some of your power budget maintaining the vacuum with a pump.
maybe vacuum insulated panels.
A big thermos would be much more challenging, though there are already long vacuum bottles/tubes used as solar cookers.