I've had plenty of trials for saddle-bags from off the shelf trek types to general shoulder carry bags. But I wanted a bag with foil lining to keep the dairy and cold fods cool after shopping. So I bought a couple of $2 supermarket cooler-bags and set to work. Starting with a steel bicycle carrier already modified to fit the bikes frame, the first step was to add an extra strut towards the rear at either side of the carrier. This was fabricated from 6mm mild steel rod with the top end welded to the carrier rails and mounted to the drop-outs at the lower end. This would keep the bags away from the spokes. To secure the bags either side of the carrier I welded mounting plates of 1mm steel sheet cut from an old washing machine body. These were then marked and drilled with a 6mm hole 20mm down from the carrier top rail. Securing the bags to the carrier mounting plates would be via 4 of M8 x 25mm brass bolts, washers and locknuts. I didn't have suitable alloy strap on hand, so I trimmed old timber slats from a discarded pantry cupboard for reinforcement either side at the top of the bag's rear panel. Each bolt would clamp a slat either side of the bag and onto the mounting plate. The images below will help explain the rest. Image 1 shows the bag in it's collapsed form and secured top and bottom with straps which were trimmed from the original bag carry handles. Each of the four restraining straps have velcro squares attached with contact cement and correspond with the opposing squares on each bag's front and side panels. Image 2 shows the restraining straps released and the bag half unfolded. Inside are the stiffening panels, currently made of cardboard but to be replaced with corflute. Tip: corflute is what many political and real estate sign panels are made of. Image 3 shows the panels unfolded and in place to stengthen each bag. The side panel sits on top of the base panel. I'm working on a way of temporarily attaching the panels to each other. Image 4 is the unfolded bag ready for loading. Note the restraining starps attached to the sides. This view also shows the slat, mount plate and fasteners on the rightside. I can carry 6kgs of goodies in each bag but 4 kgs each is more manageable if one needs to change direction rapidly.