At first it's important to know how cold it will be in winter. Here at my place the temp can drop down to about -13F (-25°C).
The second fact is will it warm up during the day or is there a continuously freeze. If it warms up the temp inside the greenhous reacts similar. If there is a continuously freeze the temp into the greenhouse drop down more and more. This is basicly to consider. Anyway more insulation is better than less.
My greenhouse gets two layers of bubblewrap. One layer is outside and the second is inside. The pieces will stick together with Scotch Tape. Over the outer layer comes a additional plastic wrap. It protects the bubblewrap against dirt. Therefor I use special brackets.
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At the inside it will insulate at the same way, except the protection plastic wrap. Furthermore gets the walls up to about 3 ft a additional insulation of styrofoam. At the end the greenhouse looks like as one of Christo's artworks.
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In a couple weeks is the time to insulate the greenhouse again. I'll try to take some step by step pictures.
One thought, drill small holes in your flat stock and string thin 22 or small gauge wire to hold your bubble wrap. This is like the way you hold your insulation under a house with a wood foundation. You can wrap the wire if your worried about it cutting into something with foam pipe wrap. You might use cloths pins to hold the bubble wrap on the angle iron. If nothing else, duct tape or the metal/foil tape. Then again, it may get too cold for the tape to work. 
