Stuart,
We had a customer in Stockton put an oven on a metal frame with caster. He had metalworking experience and wanted to move the oven around a little. Still, they are pretty heavy, so I'm not sure how often he has actually moved it.
To keep the oven light, you could construct a rigid metal tray (4") and fill it with insulating concrete. That would be structurally sound and lighter.
James |