What I have done and see others do, after you complete the actual scheme AND decals, give a inconsistant, light overspray of white or a variation thereof. Don't cover up the decals, work around them. You could concentrate on each panel and allow some of the original finish to come thru at the panel lines. To be more realistic, you could apply the thinned whitewash with a brush. If so, might want to practice first to get the effect you want.
Andy