I've used everything from inkjet transparency foils over clear acetate and Kristal Klear for windows. But Kristal Klear is my glue of choice for this purpose.
Decals; I've decaled A Pacific Electric Brass steeplecab engine, there are lots of orange stripes on the front which go around handrails, rivets and such. I had to cut the decals to small sizes and apply them with the blade of a Xacto knife. I'd also suggest cutting the decal into 3 pieces, and applying them one at the time.
Cows; Since my MOOH cars run mostly in mixed freights (and therefore empty), I prefer seeing the cows in the stock pens or in open range country.
I once tried to install a MOOH sound generator in a HOn3 car, but it didn't fit inside, and was to heavy anyway.
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