If you do this, be sure to turn the stat down on the CHE, it won't need anywhere near as much power. At the moment your CHE is trying to heat that entire room up. If your closed side ends up 3ftx3.5ft I think you will only need an 100watt CHE. See how it goes.Thank you Anyfoot for providing such detailed response.
Enclosure is 6ft x 3.5 ft. height is 1.5 ft.