Duplicating undercoating

You could try to shoot like Tamiyas acrylics wihtout thinning them from a distance. This gives you something that will look like a vinyltop and maybe that will do the trick for the chassi too?

Anyway, this is how some semi-gloss black from Tamiya looks when done this way.

Niclas

You also try it by applying a layer of putty and tap it with a hard flat paint brush while the putty is still wet. The putty will then get a textured surface.

Mind you, I have not done this before so I recommend do a test piece first on a piece of scrap plastic.

Hey Bones,

     I've read in Scale Auto where airbrushing from a little further back than normal will give a bit of texture to simulate spray-in bedliner and undercoating. This was described for 1/24 scale, but with a little experimentation, might work for 1/12. You might also try a paint called "Make It Suede". It's a spray paint that comes in a couple of colors and sprays a texture right from the can. Just airbrush the color you want over it. I hope this helps.