Andy, for the nav lamps, especially the shape required, I find that covering the 'bulb', after painting, with a drop of PVA or Micro Kristal Kleer, on the tip of a cocktail stick, works fine. Apply the PVA/KK, and 'tease' it out to the required shape. It shouls then set and shrink back to form the curve of the lamp cover, drying clear.
Noticed that the REVI reflector screen has a curved top - most I've seen for the 'F' were just rectangular, and frame-less )apart from the mounting frame at the bottom.).