I am trying to work up a bid for a 32'x32' box, 4x4's stacked 2 high (about 9" high), then filled with playground mulch around already existing palyground equipment. If I figure right, that's 3,072 sq ft. (I believe 1yd of mulch covers 100 sqft 3"thick). So I need 30 yards/mulch. Along with about 256 ft. of 4x4x12. For all you estimating experts, does this sound right.