I had this same problem using my Jackson nex-gen auto dark so this is why I stopped using it and went back to a glass lense I agree sometims i have this still on a certain angle but not to often. I say stay with the gold lense there dam clearer then anything else, I won't go to a auto dark and will stay with a philips safety lense till the day I die thanks to Henry there some dam good leses
Ok. Since you don't want any scratches on the gold lens, then you need a gap, but if the gap is small enough, it should minimize the double vision.
I would wrap the edges of the gold lens in electrical tape (the scotch 33 I use is 7 mil thick), and leave out a gasket between the filter and cover.
All lenses will reflect off their outer surfaces, and so in a multi-lens system, light will always reflect off the front of a rear lens, some of which will reflect back from the rear of a front lens and make it back as a second image. This is the "lens flare" effect you get with a camera pointed near the sun. The larger the separation between the elements, the more the secondary image will be displaced (which is why doublet lenses are glued together to have zero separation).
If you look very closely in a mirror, you will also see a second image, which is reflected off the front of the glass (the primary image is reflected off the rear silvered surface). The reason that isn't annoying, is that the primary image is so much brighter than the secondary, that you don't notice the other reflection.
Your gold lens works by reflecting, so there is much more light reflected off its front surface than would be reflected from a green filter.
Say that the rear surface of the cover lens reflects back 5% of the light, and the gold filter sends forward very nearly 100% of the light, but the green filter only reflects forward 10% of the light, then the ghost image with the gold filter will be quite visible, but the ghost image with the green filter will be too dim to see.
I've seen ghost images with my Speedglas, but they're a little different. The Speedglas is highly reflective on the front, but the cover is curved, so the ghost is distorted (smaller than the actual image), and moves quickly across your view. It is also only visible from just a couple of angles.
With a flat filter and cover, it will be the same size as what you're seeing, and will follow the image across all angles.