Tom, first I must say that this ‘37 Pierce Arrow is a beautiful little trailer, especially when combined with the car. Gorgious!!
Im not sure I understand your question correctly however... It seems that if you spray down blue, then apply rivet decals, then spray another coat of blue over top of decals, then the decals will disappear under the second coat of paint. Unless perhaps you are thinking of some sort of 3D type decal where the rivet bumps are raised, then your thought seems to be the appropriate method... but I am not aware of any kind of 3D decals. You might consider starting a new topic about this subject and possibly get some ideas stirring from a larger group of people. Maybe title it something like ‘Best way to make tiny rivets?’ ...Sorry Tom, wish I could be of better help.