i would do what ginty4141 said, but with 2 boxes made of hdpe, uhmd, or laexan. and if you want to a flat down or an up flat, or what ever you just put wood or some shit under your boxes. like to make a flat down, i would put a couple pieces of wood under the begining of the first box, then i would make the end of the first box and the begining of the second box share a couple pieces of wood, and i would leave the end of the second box on the ground.