2005 Corolla -- undercoating needed?

I have a 2-month-old Corolla, and I live in Hilo, HI, a mile from the
ocean and we get over 100 inches of rain a year (and its acidic from the
volcano fumes). The reason I traded in my previous car, a 1996 Honda
Civic, was that there was so much underbody rust damage that most of the
suspension and the brake lines needed to be replaced.

In spite of offering various other expensive "protective" treatments at
the time of sale, my dealership did not offer undercoating. I thought
the Toyota warranty would cover this type of damage for 5 years, but the
dealer orientation emphasized that it covered rust "from the inside
out", so I'm not sure just what it would cover.

Question: given the local environment, would I be wise to get Ziebart
undercoating?

Thanks.