Modifying a Compost Bin for the Desert

I attended John Zarola’s wonderful Composting Basics class last month and gained lots of valuable information. The most important thing I realized is that my homemade compost bin was too open and evaporation was high. I plan to fix the problem by nailing plywood to the outside to retain moisture but would like to know if plywood is appropriate (versus treated wood) and if so, what thickness would you recommend? Unlike the bin in the attached photo, my bin is not against a wall but sits in the open.