Stang951:

Try looking for aluminum duct repair tape. Its basically thin aluminum foil with an adhesive backing. Take two small pieces, and place them over where your painted cover is, leaving the show-through slt open. Rub down and fold the edges over, and trim the excess around the edges where the lens meets the casing. Paint over this, and you're golden. Nothing will show through the foil.

I bought the aluminum tape to use as insulation between the styrene hull and the wiring where the lighting runs are in my Tamiya. They tell ya to buy their special tape, a fracton of the length for 3x the price. I've even used it to make hinge assemblies.

If you're careful, you could do it with ordinary household cooking foil too.