Howdy,
I am NOT an "expert".
I do have a 1200 gal. fiberglass water tank, outlet 2" pipe at bottom. This tank has been in place for almost 50 years. Tank is at an elev. level that is 80-100 feet above the house. Water pressure here at the house is something like 80 psi. There have been No Problems with water storage, not even any freezing issues. Tank is tapered, smaller at bottom, etc.My tank has a top cover, top is open, not like the one in the picture.
If my tank developed a crack, I would probably use a fiberglass cloth, resin kit, like for auto/boat repair. If the tank is cracked around the bottom outlet, it may be hard to repair. I do drink the water from the tank, and my water source is a year round creek thru property, no one above me.
There was a group of us that went in on buying more than 10 of these and got a "discount", but I seem to remember "$1.00 a gal" price/NEW.