This is my first post on Gardenweb. So excuse any ignorance I may be displaying.

I built a small hobby greenhouse. I didn't do a ton of planning. Now I want to store some plants (figs) in it over the winter while I work on having a garage built for next season. I would like to keep it about 35 degrees. But I don't want to go broke (I live in Pittsburgh)!

It is 8x12 and made out of 2x4's. It has 1 side wall that is 6', to the higher side which is 9'. The roof, rear wall and sides down to 6' are covered with 8mm twin-walled polycarbonate (thermaglas). The front has 5 reclaimed casement windows I've permanently set. The rear and one side wall are covered with Smartside 3/8 sheating from 6' down to the base. The side with door has a mix of things going on - 1 stained glass window, one casement and a door made out of old windows. The stained glass and door glass are all single pane. The base is 2x10 laying on a base of gravel with 6x6 attached. The walls are built on top of the 6x6's. Inside the 6x6 I have a gravel base, then sand then recycled pavers laid inside.

So here is my question. Is it worth insulating? If so, what should I use? Whatever I do I was going to trim out the inside with some extra sheeting I have. Could I put fiberglass insulation to get the higher r-value so long as I put up a plastic barrier before I put on the sheathing (left over Smartside)? Or should I use insulation board? Or am I wasting time because all the heat is going to go right out the polycarbonate top that has such a low r-value? I guess I could add bubble insulation or plastic to the inside of the roof to help with keeping heat in. Any advice is appreciated. Thanks..Tony