Tom,
If your 3M shield on the front of your coach is already cracked, there is nothing that you can do but remove it. Polishing it will do no good because the sun damage caused cracks will go completely through the 3M shield. I have removed the 3M shield on 2 Beavers without damaging the paint, and it takes me about 2 days with a plastic scraper to remove the shield including the time with Goo Gone to remove the residual glue that is left behind. Then a quick polish with a good car polish and a buffer will make it look like new. Parking the coach in the Arizona sun in January or February when it is about 70 degrees makes the shield a little softer and easier to remove without overheating the scraper operator.
Gerald