Ahhh... the old Chinagraph grease pencil... a highly useful device in the darkroom, on the sub-editors desk and in the workshop.
Nice job on the pannier. I often think that cyclists tend to have limited vision when it comes to getting storage stuff for the bike. There are the Cobbworks/kitty litter panniers, baskets, then backpacks that are a dime a dozen that can be adapted and have all sorts of compartments. The recent and wider availability of gizmos like the ones you used has made the adaptation task much easier.
The first panniers I had were four cotton backpacks, that were souvenirs from a major motor sport event. I cut off the shoulder straps, and on each I bolted two metal tie-down hooks designed for pick-up trucks. The hooks were just able to snap over the top bar of the rear and front racks. Plastic ones would have been better, but I couldn't find them at the time (1997). I used cinch straps to tie the bottoms. I did a 3,100km tour with them. Their advantage was the big opening when unzipped, and the small sidepocket. They also could be rolled up into a tight bundle for storage. I used them a fair bit for commuting after the tour, too, and I have sometimes wondered about making up bike-specific panniers to a similar design, but with a stiff backing and some waterproofing of the zipper.