This is not an old aged discussion, it’s actually quite new.
Galvanized Sectional tanks are actually an old development, a remnant of the previous Industrial world age, Pre-world war II
Grp on the other hand is part of the early start of the modern world.
Both Grp (Glass Re-inforced Plastic) and Gs (Galvanized Steel) have their specific place, in terms of application and function. The flip side, is that Grp is more universal, that been said, if you are looking for a tank to be purposefully mistreated than, Grp shouldn’t be the selection. Ie Panels being thrown off a truck
Imagine – Composites are the new material!! The A320 and the Dreamliner 777 are excellent examples. Merc-Benz is considering using composite pistons.
If you are looking for a tank to last for a very long time, than Grp is the obvious choice….. Grp is a extremely inert material, so it’s excellent water holding material.