That idea will work very well. Here is what I built this fall to over-winter my potted plumeria and some of my hanging staghorn ferns. I built the frame out of 2x2" and used 16 mil solar blanket material for the covering. It is heated by a "base-board" electric heater, set at the lowest W possible. That heater kept the inside of this temporary greenhouse a toasty 70 F even when the garage itself was 40 F this morning. I used Velcro strips along the sides so that I can get into the greenhouse. That "door" just rolls up and Velcro strips were placed at the top to hold that rolled-up door open. There is one window that looks west, and that gives a good amount of light. If the garage door is open, light comes in from the south as well. I am not trying to keep my plumeria growing but wanted them to go dormant without disturbing their roots. I take the staghorns out of this greenhouse every week, and submerge them in the laundry-room sink filled with very diluted fertilizer.
