Have you looked a Fender Welt? My truck prior to blasting and painting had old fender welt. So we pulled the fenders and blasted and painted with fenders off and put in new fender welt before tightening down the fenders. You can order a roll from Chevy Duty that will give you enough to do the whole vehicle.
Chevy Duty The link above will take you to Chevy Duty, just select the year class of your truck and do a search for fender welt.
Hope that helps.
Chris
