As Zap said, the values were for pipe. under pressure ? ... don't know., does it matter .. not sure.. just know its a dissimilar application (tank vs pipe)
What is the volume of water, and expected max temp? thickness of the tank walls?... are they reinforced ? (bulkheads? buttressed ? by other fiberglass etc.)
All those change the dynamics... if your provide those specs, could I answer, probably not. but someone else might be able too.