I have a structure made of plywood with foam insulation that I wrap in a tarp where I keep my 'big' trachy. It's heated with Christmas lights on thermocube. The temperature there never went under freezing. The palm is growing now like crazy.
(that window is the one that the contractor installed on my front door. It's an insulated (double glass with some gas inside). I kept it after I installed a nicer one and it proved useful. This year after I decided to buy a washy to keep in the ground, I posted an ad on freecycle and I got three more for free. It's a relatively new neighbourhood, and a lot of people don't like them and change them)
For this little waggie, all I did was wrap it in one layer of some packing foam and one layer of buble wrap. It had only a very small set of Christmas lights on thermocube. I don't know what was the temperature inside, as I did not have an extra thermometer. It looked perfectly healthy when I opened it up, but with those few days of heat (it was almost 30, it looked like summer) I watered it heavy, like in the summer. Two days later it was gold again, nothing too drastically, but still below freezing.
The magnolia was a Bracken's Brown Beauty Magnolia - and it was a beauty. It was all green when I unwrap it in the spring, then it started slowly to dry, till it lost all the leaves.
I replaced it with a little Magnolia Virginiana 'Ned's Northern Belle' from
http://www.thehoneytreenursery.com/Magnolias.php
This new one is just a twig, but promises a lot
