Cardboard dash tubes

I saw some discussion on this. What I have done thru the years is go to the fish store. They sell plastic tubing of various diameters used for aquarium filters. Spray it flat black, cut to length ad you ever have to worry about decaying cardboard.

The cardboard tubes that fit behind the rectangular generator and temperature idiot lights are a flattened oval shape.

If the aquarium tubes are round, did you flatten them somehow to get them to fit right?

Thanks, Dennis.