What would be the best (and safest) way to build sideboards on a dump box (for leaves, mulch, grass, etc.)? The box has steel, 14" sides; and it has sideboard extension "brackets" but they only go up about 6" on each end. The brackets do have a hole big enough for about a 5/8" bolt. I thought about using 2 X 10's, maybe 3 high on each side, held together with 2 X 3's, then bolted into the brackets. I'm just not sure if the 2 X 10's will be too heavy. Am I on the right track or are there some better ways to do this?