undercoat/rustproofing prices and where to?

[Salanguit]

if your underchassis gets scraped on a regular basis, then undercoating may help you avoid rust.
but, in my opinion, changing your driving habits may be more effective than undercoating, in avoiding rust.

Salamat. Minsan lang nman sumadsad yung ilalim. mga 2 beses lang nmn. Siguro dalhin ko muna sa gas station at pa underwash ko muna. Silipin ko muna kung okay pa.

Follow up question: Roughly when is a car, needs another layer of undercoating or to be rustproofed? Kung marami nman nagsasabi na maganda yung factory default ng sasakyan, gang kelan ba durability nun?

Salamat