Warning: Possible dumb question

That does help, thanks a lot.

Doesn't have to be clear, but you should have a gloss coat down before the decals.  They look better on gloss than flat (to many micro-sized air bubbles between a flat coat and the decal).

After the decal is set, a clear coat over it to seal and protect.  Gloss or flat as you prefer for the finished look.

Paul

Not a dumb question. Simple answer is both. Most people sandwich the decals between two coats, this stops the decal silvering after time and means you cant damage it if you add more weathering after.

Hope that helps

Phil