its the easiest thing to make:
what i did to ensure that the cover presses uniformly, as its only secured from one end, is to file a brass washer at a slight angle, nip the one side off, and put the thicker side facing away from the cover, so as you tighten, it pushes the farthest side down first and then levels out once tight. i used some 1.5mm rubber gasket material we sue at work for milling and lathe coolant sumps...
excuse my dirty fingers, i work all day long with my hands