You don't really need a 'mold', per se, to put the silvermoons in. The reason for the boxes is to keep the silicon from 'bowing' resulting in non-uniform bars. You could just build a wood frame to go around the 4 sides of the rubber mold. Or for that matter, you could use anything, books, bricks, etc. set up against the sides of the silicon. From what I have seen, the SILVERMOONS are a lot thicker than the Upland liners are, so the bowing shouldn't be all that much. Just keep in mind that you wouldn't be able to move it if you only use a frame or other objects to keep it in shape. With a box type set-up (4 sides and a bottom) you could move it after it's been poured in.