Nothing that is made of fabric is going to prevent hail damage.
You have to remember the forces in play with hail.
Gravity + heavy chunk of ice = possible dent.
You need something that either is going to absorb all the damage, or something that prevents your car from being hit in the first place.
Think of a motorcycle helmet for your car.
Motorcycle helmet has an outer layer (shell), and then an inner layer.
Its the softer inner layer of foam/padding that actually absorbs the impact damage.
The shell deforms slightly, allowing the force to then be absorbed by the foam material.
Since no one sells form fitting covers for cars that absorb hail impacts (how in the world would you be able to carry it around with you all the time? logistical nightmare), your best bet is a garage, or portable shed.
If you own a house that doesn’t have a garage, the best you can do is install an awning, or a shed, or a garage of some form.
The next best thing is to add Comprehensive coverage to your car, and set it as low or high as you can afford to. I say this from personal experience. I’ve had to replace the roof on my house in '09, and repair one of my cars this year due to hail damage.
BC.