William Bronson ! As early as the 1st Mother earth news they showed plans for South facing ''Batch Water Heaters'' that used chest type freezers
laying on their sides and using a light reflective panel on the inside of the door - with the whole thing closed up at night (every night) by the operator
to provide an insulated storage and hot water in the morning !
I found lots of examples by Goggling ''Batch Water Heaters Pictures''
Certainly something much like this would convert easily into an insulated cold frame, making anything big enough to justify calling it a green house
probably would be a lot harder but a good cold frame should easily give you 5-6 weeks on this end of a growing season and perhaps 4 weeks in the
Spring !
Hopefully this will help get you closer to your final design ! For the good of the Craft ! Big AL
Late Note Perhaps something like this ?
http://www.webstaurantstore.com/turbo-air-tcb-5r-59-curved-glass-dual-dry-refrigerated-bakery-display-case-with-lift-up-front-18-6-cu-ft/902TCB5R.html