Michael, I'm putting a bit of thought into what your trying to accomplish and taking into consideration the area and events to which your Cat was subjected, I personally would not worry too much about panel line detail. My thoughts say you should just spray your machine whatever dark, almost black colour you intend, then once satisfied, go over the main upper wing and fuselage panel lines with a very sharp, really dark brown colour pencil. For the hull and floats particularly round the waterline use a silver colour pencil to replicate chipping and wear. Seal this in with an overspray of future or something similar. I would then follow through with the decal process, a nice shiny surface where you want to apply them. Let all this settle and then make up or get a very dark grey and with the airbrush from a great distance, give the aircraft a very, very light and quick well diluted overspray, just to lighten the blackish tone and give an effect of fading. After the first spray has dried and settled, study the outcome and see if some areas particularly on upper wing and other upper surfaces would benefit from another light distance spray to effect better shading and ware. this should also have the same effect on the applied decals, giving them a faded, worn out look.