A method for mounting a screen assembly to a screen mounting structure of a vibratory separator to effectively seal the screen assembly in place, the method in certain aspects including locating the screen assembly on a screen mounting structure of the separator, positioning the screen assembly so that crossmembers of a four-sided generally rectangular support of the screen assembly are either all parallel to or are all transverse to a direction of material flowing across the screen assembly, forcing two sides of the support of the screen assembly down with a crowning apparatus to effect crowning of the screen assembly, the support sufficiently flexible so that two sides thereof other than the two forced-down sides sealingly contact a surface of the screen mounting structure along substantially all of their length.