This tutorial outlines the way I spraypaint my stuff. I hope it's helpful. Here's the prop I used for the tutorial if anyone is interested[link] .
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If you follow this guide you should be able to make it stay that way. Although it can be hit or miss for a gloss spray. Varnish would work but I've also heard that Future acrylic floor polish works as a great clear coat for metallic paints. I haven't tried it yet myself but intend on it in the near future.