Since you decided to include more gun cosmetics in future paid dlcs, why not making the customizations easier by simply adding a menu. Believe me, it took me several minutes to figure out how to put those skins on when they first came out.
Here's how you do it in current patch. First, you go to "customize", click "loadouts", then pick you class and select your weapons. Then, in the weapon customization menu, you gotta scroll down to the very bottom, there, you will find them skins under the "aesthetic" category.
Oh, and if you don't have them equipped and saved, you will waste about more than 30 seconds after joining a match gearing up.
Now, I give it you understand why I request for a cusmization menu specifically for gun skins, or at least move them out from gun customizations, it's really isn't about the skins (let's be honest, I don't really care about them)