hg,
A better investment, in my estimation, is Eliot Coleman's original idea on this. His books all demonstrate the year-round gardening lifestyle, without benefit of additional heating. And he does his in Maine!
My hoop house that I'm building is styled on these principles. It's a frame made of cattle panels arched between two narrow outer beds, with a higher frame made of pvc pipe 20' long, arched over the outer beds. On the inside, I can hang plastic over another tall trellis, or hang it from the roof of the cp to cover the 4'x12' bed down the middle.
Then there will be a 2' tall hoop house over the bed in the middle of the cattle panel arch, and a shorter one one, about 1.75 feet tall. The double one worked out well for me last winter for carrots, beets, spinach, lettuce, and parsnips. I'm hoping that the extra layers will enable me to start tomatoes and peppers early enough to have ripe tomatoes by the first of June, if not sooner.
On one side, there will be beds for early lettuce, greens, and cool weather seedlings.
If I can get all this done by fall.
I'm very interested in the remarks he made in the video about not getting great tomatoes in the fall because of the lack of sun. I find that to be true here also, at the 48th parallel. Makes me wonder about artificial lighting.
j