It always seems counter-intuitive when you’re building a subject that will be dirty and scruffy in the end, that you now need to make it shiny. But decals will only settle in correctly, with no “silvering” (a persistent misty look from many tiny air pockets caused by a flat finish) if the whole surface is smooth. Future Floor Polish (actually I think the exact branding has changed, but the product is still available; this is a recurring hot topic in the modeling world) is the perfect substance for this. It can be poured strait into an air brush paint cup and it will spray with no trouble. This will be the best smelling step in any build. Clean up is with Windex; BUT, Future is persistent stuff. It can get anywhere and it dries rock hard. So I spray it with an old Paasche single-action brush. I’m not letting this stuff anywhere near my new brushes.