Hi Craig, hi folks.
Dont forget to consider the weigth of the tank.
300 US gal weight around 2500 pounds. A container for that much water
can weight a non negligible weight. Plus, some of the upper structure
will also add some weight that shall be held by the legs and anchors.
Jack also pointed out an important item, earthquake. An earthquake
can impart horizontal forces that may damage or even destroy a
structure that otherwise is solid enough to hold vertical forces.
Also, consider the weight of snow and/or ice if this is applicable for
your place. Maybe you will need some heating system to avoid freezing
in very cold climate.
Maybe a look at:
will also help.
This is only one of many sites returned by Google using "water tower
design" as the search string.
Jean (Johnny) Lemire from Richelieu, Quebec, Canada