I find that the fluorescent paints in use awhile ago used to chalk rapidly after exposure to daylight. The Coast Guard must have a new UV resistant paint, since their birds do not seem to do this.
For models from fifties and sixties, where fluorescent paint was quite popular, I overcoat with white, with airbrush backed off to very light flow. You need a transparent coat, just a shading. The chalking needs to be less than on the rest of the paint. If you are fading or chalking the rest of the model, do the red or orange first, mask them off, and do the rest of the model with more subtle chalking and fading.