Pooldoc, in thinking of other ways to accomplish the concept you described what do you think of this idea? Make the bag using noodle floaters around the outside while applying the inside part of the bag to the fiberglass pool wall with velcro. It would be easily removable for cleaning and would do no damage to pool. I have researched Velcro and found it works under water and can be sewed to the bag. The only part that may be a challenge is finding some with adhesive backing that will stick to the pool wall under water.