I had two banana Plants out last Winter and I saved them by buying some wire mesh,( that they use to re-inforce Concrete slabs),( it's 6"x6" Mesh). anyway I made a circle about four foot Dia. and 5' high and anchored it down with a couple pieces of re-Bar, drove into the ground and tied to mesh with tie wire. then on Cold nights I would cover the Mesh with one of those "Frost Cloths",( from Lowes), then cover that with Plastic sheeting, stick a 60 watt. Bulb down at the bottom of the Plant and kick a little loose Hay around the bottom, to seal out any drafts. I got two spots frost bitten, where the frost cloth was in direct contact with a leaf, but didn't loose a single plant and we had several nights in the low Twenties. As you know though, it only last for a few hours, until the Sun comes up and warms back up. Then I would have to run out and un-cover them, LOL. My Wife said she was jealious, I told her it wasn't anything personal, just a Farmer thing,LOL........