Gregcz1 and others,
I've been painting and lettering with decals for some 50 years now, and have made a lot of changes as newer and better paints and decals have come to market. The one thing that has been a constant, is to give a CLEAR gloss coat over the model before I decal it.
Semi gloss does not do as well, and even if the paint is marked gloss, I find that model paints do not have a good gloss to hide the decal film. Maybe some of the rattle can paints have a higher gloss to them. I don't know as I prefer to stick with model paints as the pigments are not as thick and do a better job at highlighting the details on the model.
So even if I use a "gloss black" paint on a model, I still hit it with a gloss finish. I believe that this results in a much better finish before I decal it.
I finish most all of my models with a dull finish or semi gloss finish, sometimes mixing my gloss and dull coat 50/50. It all depends on what effect I want my model to look like.
One other thing. I always wait at least 24 hours between paint finishes. And I wait 24 hours after the gloss coat has been sprayed before I decal, then another 24 hours before I spray the finish coat. Overkill? Maybe, but not for me. I know others do it quicker, but that's me. I have the time and I want the paints to cure properly.
RAY
Attached is a sample of an HO model I painted a couple years ago, the deal film in the slanted "Great Northern" lettering has "disappeared".