the stories and concerns of DEF going 'bad' while in your tank is probably overkill, as with many other 'rv' related stories. We've used the W*mrt 2 1/2 gal jugs for over 4 years now, and have never had any issues, and yes, our coach has sat for 'months' during the winter with no issues.
I actually have only used the 'pumps' once, then realizing that it's just much easier and simpler to carry my own jug, and pick up another at the next big box store. No issues.
If it makes you feel better, when you purchase the jugs, check the seal under the cap to make sure it's fully intact.
'14 Palazzo 33.3 bunkhouse 34' diesel
KingTailgater2 Dish HD, 100w/5a SOLAR, BlueOx
100,000+mi since '14 - US, Alaska, Canada - Hiawassee, GA! (also, '14 Gulfstream Amerilite and '07 ForestRiver Rockwood) : )