you live in Louisiana. there's not enough winter down there to need road salt. unless you go cruising along the salt water levees a lot, which would be my guess as to how you're getting salt on the undercarriage. don't you just love commercials where they show someone in a new pickup or a new sports car zooming around on the beach, in and out of the surf, slaloming around....
that's car cancer for sure in the making right there...
my chevy was new in 1998, and it's a little rusty, more dirty than anything. been to the coast numerous times, but i always stop off some where on the way back and hit the underside at a car wash with just water.
wash the underside of your pickup periodically. touch up paint it wherever it needs it. don't worry, be happy. hey, you could find someone with a car lift, like an outdoor one at a muffler place, for instance, let 'em lift up your pickup, and powerwash the bottom of it good with a power washer. just a thought.
peace, love, and gumbo.
-tom