Welcome to the forum. I have a little experience that may help. From northern Idaho where they spray the de icing/brine/salt and it east away at everything. I brought a clean CA truck and researched till my eyes bled. Three years later its paid off itself 10 fold...
Woolwax previously called fluid film is the only one that wont crack/cause rust to get trapped and get worse. Stay away from zietbart. Woolwax doesn't dry, doesn't have solvents and goes on like a thicker fluid like chapstick or thinned out Vaseline. It does collect dust and dirt but my truck is 99.9% rust free and I just gently rinse the undercarriage off after winter and reapply any spots that got rubbed from hardsnow or harsh wash off spots. the first time you'll use half a gallon to get in every knook and cranny then just reapplay a little every after winter.
They sell a sprayer gun and I now undervoat about 30+ vehicles before every winter. some friends/family and a few folks from work who I helped them out and now they have me re-apply every year.
Research it for youself and don't just trust me the guy form the internet. You will not be disappointed. They sell it in clear/black and aerosol cans. It only took about 8 cans to do my truck before I got their sprayer and a 1 gallon jug and used my at home little 21gal air compressor. Works great!
As another guy from the internet, I concur with Justin. Iíve tried many types of oils, ziebarts, other shops that use various stuff that harden up and lift off. Best results Iíve heard of are fluid film. The only other stuff Iíve used for initial coating (inside areas, doors, fenders, everywhere - take doors panels etc off and spray inside) is LPS3. It dries to a waxy film and seems to stay put, give it time to cure. It doesnít crack and lift, it stays greasy/waxy. In fact, Iíve used it on the front of hoods where there are rock chips etc, and you have to really work at it in the spring to remove it. But, itís very expensive, too costly to use every year.
There Is a guy on YouTube who tested various oils and coatings etc. And fluid film held up the best. Iíve never heard of it as wool wax myself, must be a new name for it.
I do the same thing as Justin every spring and fall. Clean the best you can in the spring, wash down every square inch underneath and in all the crevices, and spray it back down in the fall. Eventually the oils build up and you get quite a thick coating of it. Itís messy, but works. Slows down the inevitable. Iíve a Ď96 f250 for a plow truck thatís been in service here every winter seeing salt, that has been oiled every year. Various types of oils for that one. The oil attracts dust, dirt, and everything else. Itís ended up making a greasy dirty thick coating underneath and inside all the fenders, rockers, doors, hood, etc etc that have preserved it. I scrapped some off about 5 years ago, it was about a quarter inch thick. I should have left it, but started over again spraying it down.
HHS2000 is the other lubricating oil I like for salty winters. Itís a grease basically, with solvents. It penetrates, the solvents evaporate and leaves a real greasy film that seems to really stick and stay put. Good for hinges etc.
There are a lot of people in my area of northern Ontario, Canada that have simply given up, and expect there vehicle to simply be rusted out in 10 years. Years ago, cars didnít go 10 years before they rusted out.
Anyway, fluid film is the best stuff Iíve heard of too. Clean it once a year, after all the salt, and spray it down with it everywhere. And do the best you can to keep it sprayed down and clean of salt. All the undercoating stuff hardens up, cracks, peels off, and eventually lets salt get underneath it and traps it against the metal.