Here in The Deep South, we have few (if any) serious concerns about vehicle corrosion. With our typically short, mild Winters, the roadways/bridges are seldom salted. A Ziebardt franchise here, it would never fly.
But with my being a fanatic about rust prevention, here's what I have done, in the past:
On a HOT, Summer day....
1) Put the car up in the air (on a rack). Wash the entire underside, with a pressurized (hot steam) washer. Then, drive the car, to thoroughly dry it out. I might even let it sit outside, a day or two.
2) Put the car back in the air (on a rack). Spray the entire undercarriage with 3M Rubberized Undercoating. Yeah, it's about $5-to-$7.00 per can. But IMHO, it's also the BEST commercially-available aerosol undercoating that money can buy. You'll need between three-to-five cans, depending (of course) upon the size of the vehicle.
Expect to get yourself FILTHY NASTY. It's absolutely the worst (dirtiest) work I've ever done. Also well worth the time, labor, and money invested. After all, how much is your "ride" worth, to YOU?