I also live in salt country. Does undercoating Work? Absolutely it does. Is it necessary? That depends on how often you want to wash the salt from your vehicle.
I have not undecorated any of my personal vehicles in the past 20 years, and I have also not had any corrosion issues whatsoever.
With that said, most of the fleet vehicles at work are undercoated, but not all.
The difference: The fleet vehicles that have been undercoated on an annual basis have lasted longer than the ones without undercoating, but the salt eventually penetrates the undercoated vehicles.
My personal vehicles have outlasted all of the fleet vehicles (specific to corrosion).
Undercoating is simply a barrier that buys you time, but salt will eventually penetrate if not washed/neutralized.
My personal vehicles, I have washed them thoroughly and frequently when exposed to salt. Not letting the salt sit for long is key to success.
If you don't like washing the undercarriage, or if it's simply not practical for you, then I would suggest to undercoat. However, if you enjoy working on your own vehicle without getting covered in grease, and you don't mind spending the extra time and $ washing your vehicle, then don't worry about undercoating.
We sold a specialty piece of equipment to a customer up in Norther Canada (Nunavut). The equipment is sheltered indoors, but due to their process, it's exposed to ocean water mist.
The equipment was coated with a marine epoxy (over 200k for the epoxy) and many of the fittings, valves, hardware, hydraulic hose crimps, etc, are made of SS. The equipment is only two years old and at least 40% of the epoxy has been penetrated and the exposed steel is starting to corrode. Many of the SS fittings/hardware have started to corrode. The mist coats the equipment, it crystallizes, forms a scale and then just does what it does best. Destroy!
Point being, no amount of protection will forever be resilient against salt. It needs to be washed/removed.
This particular case that I just described has given me a new appreciation for just how corrosive salt can be. Get it off your vehicle!