It all depends;- for a small tank you can use some circular bracing. For a larger tank you could build the external cladding around the tank, using various supporting methods. Then fill in the gap with insulation material. Obviously, you cannot use large strakes of cladding, unless you can make sure to fill in correctly the gap.
I suggest to use the corrugated cladding, because it can offer a good circular flexibility and a better vertical stability (similar to the building the circular corrugated iron water storage tanks).
You also can build around the tank a self supporting structure, for the support of the insulation material.
It all comes down to the buck;- if you have enough, any of this might make it for technical solution, otherwise this will become a big symbol for wasting money.
Cheers,
gr2vessels