With your 2'x 3' structure, you will want to completely open it up during full sun days. Since your back door is of a good size, open it fully. If it is still too hot in the day, you may want to put something over the top to provide some shade to keep the temperature below 90 deg. Actually any thing, even newspaper, will help cut the heat gain in your relatively small structure. Get a thermometer and if the temp. is going over 90 deg inside, put on some shade. Keep adding more during the day if necessary to keep the temp. below 90 deg. if possible.

Did you every find one. I am looking for one also? I saw the Thinking-outside smart greenhouse at Sams years ago but my house burned down I had to move. Now that I can buy one I can't find one. I would build one if I had pictures. I love the design. Any help?

There are likely cheaper options for initial price. But over long periods the cheap option will likely fail when needed most. And cost per hour could and likely would be higher over long run.

A simple hoop house works well to shelter your plants from weather and is so inexpensive. I use EMT conduit overlaid with poly tubing, 2 X 4s and 4 mil plastic. All available from Home Depot and Lowes. The plastic is held on by clamping with 2 pieces of poly or pvc and poly pipe. Simply cut out about a quarter of the larger pipe, lay the plastic over it and insert the smaller pipe. The guys in the plumbing department can tell you which sizes will work.