Rainer
Contributor
A real issue is when the tank is rolling around and gets a plenty of scratches on an exterior over time, specially in the SALT water environment. I don't think it will matter on the fresh water though. HDG lasts long in any circumstances.
You don't seem to have a very good understanding of how painted galvanization works. Even with scratches, rust won't spread. That's the entire point of the process. You can also buy galvanizing paint to patch up any scratches you'd find. While I, too, rather have HDG cylinders, your post suggests you're missing something.