I would use foam for walls instead of wood. Get the shiny stuff for light reflection and easy cutting. It resists heat as well. You would need a wood frame true enough but the foam may help. Or what I would do is sleep on the coach and just line the walls with mylar of your bedroom. Pond liner is great to air tight the rooms. Basically I think you know what you are doing and will have much success. You can always go bigger or start big and save on labor. Nugs go quick.
One love
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