I use the bag as above and hang it by the two handles from the garage rafters.
I then use two lengths of seat belt type webbing (bought on ebay) and use this to suspend the back, from rafters either side of the roof, so that it hangs parallel to the floor leaving space to get a car into the garage. It does need two to do this though.
Lastly, I cut holes in two tennis balls to put over the "bayonet" fittings to protect the bag.
After three, maybe four years of doing this the roof hasn't warped or twisted and remains in perfect condition.
HTH
