The problem with painting everything in gloss first, then using a flat overcoat after decaling is that many colors appropriate for military subjects are only available in flat.l In that case, most of us apply a gloss coat, then decal, then dullcoat. If the color is available in gloss, fine I will use it. If it is only available in flat, I use the above procedure. If you want to use only gloss as your base coats, you'll need to become accomplished in color mixing (which is actually not a bad skill to acquire).