Rambler made a custom frame bag for me. It is amazing and I love it. Here’s how we did it:
To make a pattern:
1: I cut a large piece of brown craft paper (you can also use butcher paper or a flattened paper bag)
2: I used low-tack blue masking tape (don't use duct tape or gorilla tape!) to hold the paper against the frame
3: I traced the space where I wanted the bag to live (use a pencil, not a Sharpie)
4: I cut out the pattern and traced it onto a piece of corrugated cardboard
5: I wedged the pattern in the frame and marked the spots where I needed to adjust the pattern
6: When I had a good fit for the flat pattern, I built a mockup: you can see one of the mockups is too big and bumps against the water bottle!
7: I went for a few test rides to check fitting, leg clearance, access to water bottles, etc.
8: I sent the pattern and photos of the mockup in place so Kuba knew where to place the daisy-chain attachment straps
…and Kuba did the rest!