I like the way this guy put sides on his utility trailer. I borrowed many of his techniques when I did the same thing to my four by eight trailer. I only had OSB, so painted it will an oil based paint, and used mechanic's wire to hold it together at the seams. I also inserted two by fours into the stake pockets of my trailer, and used wood screws to attach the OSB to the studs. OSB doesn't like the elements, so my next project will be to replace it with treated plywood.