Fiberglass is a lousy insulation and duct taping it on to a garage door you'll have it falling off within a year.
Garage doors are also known for being drafty, fiberglass insulation works better as an air filter then as an insulation, so you'll at least have clean cold air coming in to the garage.
Something to try would be a single sheet of 6mil plastic glued to the back side of the garage door, it wold stop drafts, create an air pocket to insulate and it would hold up better then duct tape on paper on a moving door.
Green Hinge System Residential Hinges
would be the other thing I would try, they keep the closed garage door tight to the doors frame when closed.