Generally, acrylic floor-finish gloss coats are airbrushed onto the entire model. Then, once the decals are on, the model is airbrushed AGAIN with a top-covering coat (flat or gloss) to blend everything together. Since it sounds like you will be hand brushing, let me make a suggestion or two.
1. Try buffing the paint out, first.
Using a T-shirt wrapped around a finger tip, rub the paint finish enough to knock back the flat "grain" and produce a satiny smooth surface. This may be enough to prevent decals from silvering, but don't buff hard enough to wear off the paint!
2. Trim all decals closely with a sharp #11 hobby blade, before dampening.
By doing this, no excess clear carrier film is left to show any silvering. Don't cut through the backing paper, just cut the decals away from any carrier film that is seen around their edges.
3. Lightly apply the Future only where the decal will sit.
4. Get a spray can of Testors "DullCoat."
Overspray the model after applying the decals, with a couple of light coats of the DullCoat. You will be astonished how the decals blend into the surface after this and appear to be "painted on." Remember to mask any clear parts prior to overspraying.
This may seem like a lot of extra work, but the results are worth it. This is the way most of the really great models you see, and admire, are done.