The oven is basically done. The lid's on, temp controller and thermometer are working. It heats up to just over 400 degrees in 1/2 hour with both elements running (both on one 15A circuit, which is not a good way to do it, only used for this test). It'll probably heat slightly faster when I move the oven closer to the panel and use two circuits. It's not great performance, but pretty good for 110V.
If I only run one element (1500W) it heats up to about 335 degrees in one hour and stabilizes there. So that answers THAT question
I guess this means it's possible to a) build an oven out of aluminum and steel studs/tracks, and b) you can run it on 110V, using two elements on two 15A circuits. I think both are compromises, if I had more electrical power available, I think I'd forget all the tricky insulating and just brute-force it, using steel and more/bigger heating elements.
Aluminum doesn't seem to be a great material to use because of the expansion. It worked here, but it was a pain to build because of having to insulate all the inner panels and drilling the oversize holes.
But with the power limitations I have, that's probably the only way it could have been done. It is pretty darned efficient, the outside doesn't get very warm at all.
All that's left is to put a couple of latches on the lid to seal it better while it's running, install a couple of rails to hang parts from, put a chain on the lid to keep it from opening too far, and if necessary, install a fan. And maybe a small vent. And maybe a small window with a lid, like Jim did.
I'm sure glad this is done, it wasn't a very fun project at all! I'm not sure why.