Homebrew PCBs

I'd like to improve the efficiency of my cheap toaster oven.

I suspect it is like all ovens - a thin sheet metal oven in a thin sheet metal enclosure.  And no thermal protection around the control electrics.

I'd like to use a thermal insulator, either wrapped around the oven, or just something stuffed into the gap between oven and shell.  I'd also like to protect the gap on the right where electronics will go.

Any idea what kind of cheap insulator I can use for that?  I've used ceramic blanket before, but a strip 50mm wide was very expensive.

Is household fibreglass insulation wool capable of withstanding the 300C+ temps?

Thanks,
Frank