Instructions called for positioning with crown down. I used similar clamps as shown in you tube video. Could not eliminate gap. Mine was obviously bent in shipping and I will have to bolster up the edges.I’m going to use 2x1x.188 C channel and form a 2 inch edge rather than a bare 3/16th edge that will undoubtedly bend. I cannot finish welding the ribs underneath until I complete the perimeter. Hopefully I can get most of the bend out although I highly doubt it will ever be “flat”.