We added plywood doors and some additional protection for the nest boxes from blowing rain. This design allows for easy access to eggs. The nest boxes will be lined with straw.
You can close in as much as you want of your chicken tractor with plywood or other scrap wood, but remember that the more you close it in, the less ventilation it will have. For an A-frame shape, the ends of the As will be the main ventilation for the entire coop. For a box shape, you can have all four sides open, or shield two sides against the wind and for some structure to hold nest boxes. It's a good plan to have two opposing sides open for air flow-through.