I don't think it's the salt drying the undercarriage that causes corrosion. Isn't it a chemical reaction caused by the salt itself? That said, you can wash underneath and spray a bunch of cheap wd40 under there once in a while. I do that to my cars since I'm near the beach. I hit all the rubber and nuts, bolts, etc. Also anywhere it looks like rust might start. Not a professional opinion here, just trying to offer some advice.
As far as stripping wax goes, if you're doing it before a good detailing, I have had good luck with highly diluted degreaser but have also used dishwashing liquid. Just don't allow it do dry if you're using any kind of degreaser. I haven't experienced it, but have heard warnings of possibly streaking the paint. I usually do a lather, rinse, repeat process with pressure washer to get as much stuff off the car before clay barring it. Then polishing if you want before a good coat of paint sealant and you don't have to do it for quite a while again. I use spray wax every time I wash my car.