I have done a little research and have concluded the following:
AIR IS IS THE CULPRIT
Diesel reacts with oxygen in the air at the top of the tank and forms sediment and gum. Water condenses from the air, and algae, fungus, or bacteria grows.
ADDATIVES ARE FOR VENTED TANKS
Addatives protect diesel stored in vented tanks in lawnmowers, recreational vehicles, motorboats, etc. The engine is ran only part of the year, typically during the summer months, and the fuel remaining in the tank after the season is over needs to be protected until the next season comes.
ADDATIVES NOT NEEDED FOR SEALED TANKS
In a sealed container, a small amount of air is deliberately trapped inside the container to allow for expansion of the fuel. A tiny amount of sediment, gum, algae, fungus, or bacteria forms after the container is filled and sealed, then the air becomes "stale" and no more sediment, gum, algae, fungus, or bacteria forms.
DEHYDRATION NOT NEEDED
I have driven 10,000 miles since I installed a Racor water separator in the fuel system of my 6.9 van. No water has accumulated in the separator, so it appears the fuel I purchase is fairly dry. It does not appear the fuel needs to be dehydrated before it is stored.
WINTER OR SUMMER FUEL?
Which fuel might be best for long-term storage, winter or summer diesel?
ARTICLES
British Petrolium article "Fuel News: Long Term Storage of Diesel"
http://www.oilburners.net/forums/attachment.php?attachmentid=44524&d=1365177792
Wikipedia article "Galvanization"
https://en.wikipedia.org/wiki/Galvanization
AR15.com article "FUEL CAN ORACLE"
http://www.ar15.com/mobile/topic.html?b=10&f=17&t=643480&page=1