Why don't you just root in a bag instead of airlayering? I don't think that roots would grow well for you since you are going to have it in a cold garage or storage place. Roots need lots of heat about 75-80 degrees. I just rooted six cuttings off of a dormant fig and within 2 weeks, they rooted, but the key was it was 85 degrees in front of a space heater where they rooted. Just use the rooting in a bag method Jon teaches, it works very well. I think you'll waste your time fooling around with them in the conditions you are describing. If you want to air layer, try next year or else do them in a WARM location. Why don't you just bring the tree inside, depending on the size, and keep it in a light window with very warm and airlayer it there. Ciao, Maggie.