I purchased a 5' 5" x 10' utility trailer and want to add sides to it. It has 12" high angle iron sides, but it is open and I want to extend the sides to about 20". I was thinking about using 1/2" plywood (to keep the weight down), but wanted to know what kind of plywood to use. I know they make several types of exterior plywood. Could you please advise me on this? Thanks!!!