Some guys use Rustoleum on their undercarriages. Personally, I don't mess with it, and I'm in WI, where the road salt is around for about 1/2 the year.
What I've always done is, whenever I get a rare winter day that's not gonna be too cold (next Tues is supposed to be almost 40 here), I go up to the self wash (the drive in coin kind...don't use brushes, those flat sudsy strip things, etc, on your Jeep) and hose the salt off the exterior, and make sure I hit the underside really good, as well.
I drove a Jeep Liberty up here for eight years and did that, and it was fine.
Of course, first nice spring day, I do the same thing at the self wash, then bring her home and do a really thorough cleaning, wax, etc.
Then it usually snows on us one more time, but still...
I've never seen an undercoat job that was thorough enough to do anything except instill a false sense of security. The best thing to do in the Salt Belt is to wash it frequently and completely (yeah, that means crawling under it at the car wash). Lucky me, I work in a shop, so I put it on the lift once a week for a rinse if they're really dumping the salt.
A forum community dedicated to Jeep Wrangler owners and enthusiasts. Come join the discussion about reviews, performance, trail riding, gear, suspension, tires, classifieds, troubleshooting, maintenance, for all JL, JT, JK, TJ, YJ, and CJ models!