Roger, those blisters are probably from some over anxious yard monkeys not knowing how to use a heat shrink gun.
I've heard highly informed and expert opinions both ways. The shrink wrap was cut back to the sheer after a couple years and the damage is mostly on one side (the sunny one as she was sitting) so I suspect moisture entrapment. She was laid up with the stick in so plenty of water could work it's way down under the shrink wrap.
Fortunately, it is amazing how invisible even major defects like this are from 10 feet away when the boat is in the water. Even when they were on the dock side the first couple seasons, I never noticed them. Since they got me several grand off the purchase price, without which I wouldn't have the boat, I kind of like them.