So it's probably not a humongous container. And if you don't really need a greenhouse all year, they are tedious to deal with all the time.
At any rate, if I'm visualizing correctly a large container, I might think about a kind of hoop house, a portable one made of PVC that could be set over it and easily removed in changeable weather. Search the Internet for "greenhouse dome" and "umbrella greenhouse." I could even imagine some circumstances and containers where a large clear umbrella could rest across it or have the dome of the umbrellas resting on slats laid across the container. I wouldn't think blueberries would need more cold protection than that. I suspect they would appreciate the air movement up and through the spaces.
