I run the fuel out of the jug down to the last drop, my current fuel jug is more than 2 years old, it was stored 1/4 full, and runs fine. a nitrogen blanket is often used in storage of methanol in large quantities, but it's not to protect the methanol, it is generally used as a safety feature, nitrogen is chemically inert and is heavier than both oxygen and methanol vapor.
Usually the problem with our fuel is that it has absorbed too much water from the atmosphere, the water vapor absorption properties of methanol is so great that it is safe to say; if it's exposed to atmosphere, it's absorbing water. Evaporation can be an issue also, but Methyl alcohol has the slowest rate of evaporation of all the alcohols.
I would note a few precautions I take to prolong the storage life of my fuel. 1) I always put the unmodified filler cap back on the jug when I'm not fueling, it only takes a few seconds to switch caps. 2)I Keep the fuel container out of direct sunlight. 3) I keep the fuel containers stored in a cool dry place when not in use, not in a hot garage, but a cool dry place.