Honestly, not much is needed for long term storage if you buy clean, dry fuel, put it in a clean, dry, unvented container, and store it with the conatiner nearly full with little air to allow condesation.
Water is the enemy, and water causes most of the problems with stored diesel.
I have run 12 year old diesel stored like that with no problems.
That said, Pri-D is a good insurance to add and is not very expensive. It works like a champ. If your container has some residual sludge or water and you can't fully drain and clean it, or you think some water may get in, a biocide like Bio-Kleen could be warranted. But in 99% of cases I would say some Pri-D would be more than enough, if it is even needed at all. But the Pri-D is a good all-around additive to it is worth using regardless.