Get yourself some aluminum tape in the heating and AC section of your local home improvement store.

Aluminum paint is very opaque.  Aluminum dope is sprayed as the first coat of color on doped fabric on real planes because it prevents most of the UV in sunlight from penetrating to the fabric.  Any paint with aluminum powder pigment is good at stopping light.

I've never lighted a ship, so I've never tried this, but the thought occurred to me.  Spray the insides with a coat of flat black, then spray a coat of chrome silver.  The black under the silver should provide a kind of mirrored surface effect, concentrating the light while blocking it from showing through the plastic.  Has anyone tried this? 

John

You could also use aluminum foil to easily cover flat areas as well as irregular shapes. It is absolutely opaque and reflects light too. Use foil adhesive to make sure it stays down.  HTH

I've used black paint (several coats) followed by white to help reflect interior light. I've also used black Tulip paint. I believe its primary use is for raised lettering on clothing. Its not found with regular paint.

I've also built light boxes as littletimmie mentions.

Just depends on the project.

Flat black paint is your friend.

You could also (if theres enough room) build a box around the light on 5 sides and back the light with tinfoil. This will make the lights Very bright.

Test first..... sometimes bright light can be bad... very bad!

Yeah, the fairly small things I've lighted I've had good luck with black spray paint too. 

I did one of those with the lighting kit and I sprayed everything inside that wasn't a area for glue black.   then tested it by temporarily assemblying it and seeing where it leaked light.  once it was all glued together  I shot black on the outside aswell.  Lots of taping off area's which was kinda time consuming

John