A warm place for the plants to winter

Well it doesn't look like the garden shed/greenhouse will be finished before the first frost, so we are constructing a temporary cinder block space to house the plants and keep them at least above 40 degrees.
To build this structure we used the fiberglass frame from the shower as a guide for the width. Cinder blocks were dry stacked (with-out mortar) on the sides and a few in the front for strength. We then placed the fiberglass frame with yupon holly sticks as the support for the plastic that encloses the whole structure. The important thing to pay attention to is not allowing any air to escape, it will surley be the warm air you want to keep inside.
We heat the space with two 75 watt light bulbs and when it gets below 28 degrees or so we fire up two kerosene lanterns. All the plants fit and It really does work!