Humidity is important. Is the pole barn cement floored? If it is dirt you are fighting an uphill battle. As temperature rises and falls, the metal on the bikes will act like cooling rods and actually condense moisture as the outside moisture rises and falls all winter long. Snow, melt and then super cold and then a warm front will do a number on anything that has metal on it. If you don't believe me, walk into your barn in the winter time after a warm front walks thru or cold turns to rain. You will see condensation on the metal several times thru the winter.
So that doesn't mean that you can't store it out there, but you have to insulate the area you intend to store the equipment in. Then install a good heater, and easiest is electric. It doesn't not have to get it very warm...probably mid to high 30 degree range would do it. This keep the bikes from the deep cold which will produce the condensation on the bikes when the warm fronts walk thru.
If the building has no cement floor you have to be sure to keep it warmer to prevent the moisture from forming.