Per Cat and Cummins, there are two times that additives are recommended:
Storing summer grade diesel (#2 diesel) into below freezing temperatures. So if you fill up in the summer or fall, this could be an issue. BTW filling up before storing is HIGHLY recommended as it reduces condensation.
The other recommendation is if storing diesel for over 2 months in summer or 3 months in winter, add a BIOCIDE. You can find them at any marine store, as boats have the same fuel storage issues as do motorhomes.