Exposure 2 should be used only where it’s dry. As for cost, prices for a 4×8 plywood sheet range from $10 for CDX to more than $50 for knot-free hardwood veneers. GETTING THE BUGS OUT ...

Use 2 1/2-inch long bolts and screws. Use CDX plywood at least 5/8 inch thick. Place plywood over window, allowing a 4-inch overlap on each side. Space bolts or screws 12 to 18 inches apart.