Hi, due to limited space, I am building my oven into an enbankment, directly off the back patio. This saves both space and time, but also means that the concrete base will likely sit directly on the earth, with a minor brick wall surround to support and contain the setting concrete. My issue is this : as the concrete is not suspended above the ground (like generic ovens), but will sit directly on the actual earth, I suspect it will be a bigger than usual heat sink. Should I therefore put some insulating layer (of what?) below the concrete base. Or simply make the insulating layer above the concrete thicker. Any suggestions would be welcome. We live in Melbourne Australia, so the climate can be cold in winter, so want to ensure the oven is as efficient as possible. Thanks for your advice.