Another trick is to paint your fenders then get some Silly Putty. Stretch it out so it is flat, about 1/16th inch thick. Place it over your fenders and work the Silly Putty up to the edge of where the body and fenders meet. I use an paint brush handle with a rounded edge to push the putty where I want it. Don't flood the body with paint when you spray, building up light coats works really well. When you are done just peel the putty off your fenders, you can reuse the putty. The best part is you can pick it up at Walmart for a buck or 2 and it does work really well with some experimenting and patience.