For making the screw holes in gasket material I use a hollow punch and mount it in a drill press or hand held drill, place the gasket material on a flat board, the rotating punch will make a perfect hole without tearing the material. To get a very nice outline of the case transfered to the gasket I coat the case with water soluble block print ink, it does not dry really quick so its easy to work with. Once coated take the wet side of the case and place it directly on the gasket material, careful not to cause it to swerve just push down lightly, then lift straight off. Presto, there is the gasket shape in near perfect outline, holes and all. Cut out as described before, holes first, inside next and after confirming a good fit up trim the outside a bit large to begin with, after assembly the outside can be trimmed flush with an exacto knife.