This was a fun project. Karuna saw Gabes heavy porteur and decided she wanted something similar for commuting on her motorcycle.
We decided to make it a rolltop and give it plenty of space for lots of stuff. The challenge was getting it to fasten to the tiny back rack on the rear of her bike.
After many attempts and modifications, the motobag ended up with a hard bottom to make it snug on the rack no matter how much (or how little) it has packed. The hard bottom is two sheets of 1/8th inch particle board sewn in between the inner and outer layers - over which there's some padding to keep that cargo comfy!
There's a shoulder strap, which doubles as a tie down. On the bottom, 2 inch webbing slips over the rack to hold the back in place. And in the back there's two cinch straps that pull the bag back and keep the jiggles at bay.