Just some quick thoughts is all I have:
1.You can cut the GEL into a diameter that will fit down inside the tube. It is a material like mylar sort of. A thin sheet stock of colored "plastic".
2. If you find something that fits you can paint it with amber light bulb paint.
3.You can drill out the middle of one of those green caps in your link, leave a lip, and glue gel or equivalent down inside on the lip. That way it fits the tube.
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
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