So what is a "kitbash" you may be wondering? The traditional way that filming studios built these models was a varied process, as you woudl imagine. The model shop received detailed conceptual artwork and an armature was constructed from blueprints. They would usually make the inner armature from wood that mounted to a metal pipe system with multiple mounting points, so that the model could be filmed from different directions. This was then "skinned" with acrylic or styrene. Sometimes the armature was made solely from the acrylic as it does not sag or warp the way styrene can. Once they had the armature made, the detailing was added with bits of sheet and rod styrene stock and many many pieces from model kits (tanks, planes, trucks, etc). This was the process known as "kitbashing" - taking many kits and breaking them up for their parts.
Kitbashing wasn't haphazard though. A process emerged that has been called "Boilerplate technology" - it's basically a method to the madness, where the parts are arranged in a way to suggest functionality. If you have an engine-looking area, add venting and cooling hoses. If there is a section of detail isolated along a plane, run some piping to the cluster - and suggest that the piping runs power to a diifferent location. Add armor plating to break up the flat surfaces. suggest panel lines (like you see on aircraft). These are the things I try to keep in mind when I make something of my own. Like this:

It's a work-in-progress that will look like a furnace (boiler! haha). It's a small base housing batteries and a circuit board that fires two yellow LEDs in a random "flicker", with a housing I made from various bits, topped by a B-29 nose. Directly behind the nose is a tank drivewheel that I have hollowed out and modified with miniature domed rivet heads. I took an X-Acto and hollowed out the recessed areas, and backed them from behind with small plastic lenses I purchased in Tokyo last year. These are glued into place with a clear acrylic material.

So, the end effect is a flickering warm light that gets bounced by the lenses from above, and spills out between the sprocket teeth from below/sides. The lenses prevent you from being able to identify the location of either LED specifically, which is pretty cool. I also shot the B-29 nose with gloss laquer varnish, which gives it a "shower door" effect, mottling the light even more. I plan to add more detailing to the sides, and will paint the entire thing to look rusty with a slight patina - the "glass" will remain glossy, but the black spars will be matte/colored.