Ever use a greenhouse in the winter?

has anyone ever used a green house to grow in during the winter months? The climate I live in gets down into the mid 40's at the coldest with an occasional dip into the lower 30s. Will a portable greenhouse get me through the winter with a small outdoor grow?

 

I didnt think about that...what if I veg inside and adjust them to outdoor for flower?

 

I have a small grow box inside and I also have a healthy mother who can put out alot of clones for me. She grows out of control sometimes and I end up pruning and throwing alot of cuttings out. I wanted to experiment with some outdoor stuff this winter, to include some veggies from my garden. I wanted to grow some items in global buckets...so I was wondering if I use a greenhouse set up, if it would work out for me. We dont get slammed with super cold weather in the winter here so I want to check this out. What I wonder though, is will the green house be able to absorb and store heat that will sustain during the night when the temps dip down into the low 40s/high 30s?

 

I was thinking of going with some wooden frame parts and opaque plastic. The thing I need to figure out though is how the green house manages to hold heat? Would I need to fully enclose the structure to include the bottom?

Its all really experimental so I guess its worth a shot.