I've got a camping folding oven with temp gauge on it.
Not sure of the make and model because we got a load of secondhand camping stuff and that was in it.
fairly large though, good enough to make a loaf in say or cook a small chook.
What about a metal pedal bin that they sell in the shops?
There about 50 liters or so, tip it on its side and you've got a longish oven with door,
Or a metal bread bin that they've started selling again
Not perfect but better than nothing.
Or a lot of rubbish bins on lamp posts or on the street have a steel drum inner that the rubbish bag attaches to.
You can use the universal key available from places like wilko's that open it.
Bit of a clean and your away.
have a look at this if its in your price range maybe...
Kubex collapsible oven
http://www.ebay.co.uk/itm/Kubex-collapsi...27d05885f8
I tried to be normal once.... Worst two minutes of my life...