Over the years, various attempts have been made to make an accurate Vader helmet. The most successful attempt came from a poster named hurricane. He used a mask from the 1/6 kaiyodo model kit. The mask on that kit is very accurate in shape. Much more so than the sideshow or hot toys figures. The best dome at this point was created by hurricane but I haven't seen him on here in a while so I am not sure if he is still selling. You could possibly get away with the hasbro dome and kaiyodo mask. The hots toys mask (or air freshener that you have) and hasbro dome looks pretty good as well,