The process of getting a custom bag was simple...I emailed Judy about the bag and we arranged to sort it out at the Brighton Big Dog race. I stopped by her stool mid race (I was doing the Fat Bike pairs), Judy took a few photos and measurements then handed the bike back, it couldn't have taken more then 2 mins. As you can see from the photos the bag fits like a glove. The zip can be opened from either end which is handy, there is a divider midway along the bag (about where the top of the bottle is).
So far I have only used it on shorter rides, the BB200 is at the weekend so I will give it a proper test then.