Saw some 303 at EMS last week for 8 bucks. Boxes looked like they had been hanging around awile - don't know what the shelf life is. This stuff normally goes for about $15.
Does Armoural offer UV protection?
One thing I don't expect to do is hand the plastic yak down to my grandchildren. My guess is after 4 or 5 summers lashed to the roof of the car and it's ready for the milk bottle recyling bin.