'Did this in the Fall ('09) with much help from dwellingmates...
Early SketchUp rendering
Looking east on the inside
From the outside
Note the double-bubble-wrap w/ refelctive mylar, on the ground.
We wrap that over the top of it during the coldest spells,
and it works great. 'Getting a bit chewed up, however.
I'm thinkng to encase the wrap in some sort of more durable cover. Super-duper-pneumatic-lid-lifter
This was absolutely key to controlling temperature in the thing.
Finally got 'em installed mid-way throught he winter, and it made all the difference in the world.
Previously, we'd forget to open or close the thing, and it'd alternately cook or freeze. Spring bounty, after the glazing came off