Interested in hearing how you are getting along with bellows repair.

Here are a couple of things I've heard... The Aquaseal stuff works.
There is also material called Gutta Resist. A natural latex product used in fabric crafts. has it.
For large repairs I'd been searching for a strong, opaque and extremely flexible fabric. A friend put me onto Gore-Tex patch kits. You can use Aquaseal to glue the Gore-Tex to the inside of the bellows, and it will remain flexible.