You don't need to add a gloss coat to Scalecoat glossy paints to decal them. That's the beauty of glossy paint...(step 1) paint, (step 2) decal, (step 3) final coat either gloss, semi-gloss, or flat. That's three steps and two coats of paint. Normally Scalecoat doesn't require a primer on metal either.
With most non-Scalecoat paints many of which have a flat finish, it's (step 1) paint, (step 2) paint gloss coat, (step 3) decal, (step 4) final coat...add a primer for metals. That's four steps with three coats of paint on plastic and four coats of paint over your details on metal.
I find that Tru-Color is equal to Scalecoat as far as coverage is concerned and not needing a gloss coat for decaling, but I have not painted any brass with it yet so I don't know if it requires a primer.