I use Humbrol gloss acrylic varnish, decal, then semi gloss or Krylon matt, it depends on the a/c type. The problem may be your decals, they vary from kit to kit as regards silvering. try using a decal setting/softening solution, again, I use Humbrol Decalfix, it's cheap, last's a long time per bottle and doesn't seem to harm most decal types. Try using future on canopies, I brush it on, it gives a good shine to the plastic, almost like the real thing. good luck!