Thanks for the comments guys!
The hope behind the reverse flow is that the plate will help keep the temps even. I will be doing a burn this weekend finished or not just to see if that's true. I know it's gonna be a fuel hog with the thin walls, but it should be air tight when I'm finished so airflow shouldn't be too much of a problem.
My neighbor suggested getting a water heater blanket to help out with heat loss. Will that be enough? I don't know.
All I know is that I'm excited to give it a try! There will be plenty of pics of finished product.