I too read the DEF storage article.
We just did an almost 4k road trip in April, our next is a 550 mile road trip in June, then a 2500 mile road trip in July and a 4200 mile road trip in September. After that, our next long trip will be a 4k miler but not until April/May of 2015.
So, on the way back from our 4k trip, I noticed the DEF tank showed less than 1/2 full, so I filled it up at a Pilot Truck stop.
My thinking was that after our 2014 trips, I would have the DEF tank down to about 1/3rd full by October of this year and would refill it just before our next long road trip in April/May of 2015.
A friend recommended that I fill up at busy truck stops with DEF, due to the high turnover