[skyking]

Nice project!
I'd face the cell opening all the same direction, and make a template. Then I'd use fiberglass cloth and epoxy to make up the modules. They would be strong and light.
Put a piece of tape across the battery side of the holder to back up the glassing operation.
2 layers of 4 Oz cloth and epoxy would be plenty.
Then I'd make some sort of system that clamps each module into the pack. You could do a quick health check of each module with a meter, and pull out that module to see what was up.