Today we have been experimenting with a different way of attaching fins. One problem with tape is that it tends to leave sticky residue when its removed, it peels off when subjected to heat or water. If wrapped all around it tends to stretch or break as the bottle expands.
We are trying a couple of elastic rings around the bottle, and the fins are simply tucked under these essentially rubber bands. We have made them out of bicycle inner tubes and glued them with contact adhesive. This holds very well on the bottle, but is a bit heavier than tape. We also tried cutting a ring out of kitchen rubber glove which also worked quite well. It is nice and thin so lightweight, and there is no glue required. It is perhaps not as strong but should be adequate.
We may also use the glove ring to join the bottle separators between bottles, as these give a nicely aerodynamic shape.