screw the heat gun, scraping, and peeling. Go over to C-Max (right next to the NAPA in the NE near the Hooters), get a rubber eraser wheel for use with a drill. Use it exaclty as it sounds. Works exactly like an eraser. Use a little brake clean or other solvent to clean up any left over glue residue. I used these things years ago when I worked in a body shop, and have sworn by them since. I've even used them to strip entire decal packages off of fleet emergency vehicles.
Wear safety glasses. It works like an eraser does with a pencil and you get little flakes of rubber all over. If you have alot of decal to remove, I'd suggest "garage clothing". Also, when they wear down to the line, don't think you can keep using them past that point as you'll quickly find the plastic/metal plate in the middle for support.