I've made some tentative decisions regarding the shadowbox:
First of all, it will be forced perspective. Meaning you have a limited viewing area, and you can only view it from one angle. So instead of having a medium-sized "porthole" to look through, it will only be a slot with thick glass and perhaps a lip on the inside to further narrow the viewing angle.
Second, it will be a medium sized shadowbox, using a Star Trek Federation Heavy Cruiser (from the old Space Ship Set), and a Klingon Battle Cruiser (also from Space Ship Set). It will be a ship duel that takes place in an asteroid field. I decided to have asteroids because they are big enough to hide the supporting arms that suspend them, and they can hold the supporting arms that suspend the ships. There will be a relatively nearby star that you can't see, but it will be represented by a bright light in the shadowbox that illuminates the starships. The back of the shadowbox will be black with fiber optics to make stars. The back of the shadowbox will be shielded from the nearby star's light by a board, so that the spotlight can only shine at a certain angle, thus illuminating the asteroids and starships, and not the back panel. In other words, the spotlight which represents the rays of the nearby star will have a forced perspective as well so the backboard is not illuminated by it.
With the forced perspective viewing slot you won't be able to see the sides of the shadowbox which would look unrealistic.
The starships will be mounted by rods fairly close to the asteroids, and at such an angle that the starships hide the rods. The asteroids will be somewhat large relative to the starships. The asteroids will be mounted by rods coming from the backboard, at such an angle and location that they cannot be seen while viewing through the slot.
I'm thinking I'll have to make the asteroids with wood and milliput. Lava rocks are just too small.
Will use brass rod for the supporting rods.
Starships will not have internal lighting, but thinking about using flourescent paint for some applications.
Was thinking about using something like x-ray film of a starry background if that would be possible. I'll look into it, but will probably have to use the fiber optics.
My only concern is that the spotlight might shine on the backboard and make it look just like that, a backboard with fiberoptics. Hopefully making a slot to narrow its beam will take care of that problem.
This is what is in my mind right now. Suggestions and criticism welcome.
Thanks for the help so far
DJ