The areas underneath my truck that look best are areas that I Zerorusted then covered with the Duplicolor brush-on bedliner. The bedliner is tough stuff and holds up well to grit, gravel, and road salt. That stuff just sandblasted off the areas that were ZR alone. Mine's a 4 season Illinois daily driver.
http://www.chuckthetruck.homestead.com/page1.html