I keep my “fender” near my bike in the garage. When the road looks wet or threatens, I can easily slide the folded-over old long stuff sack (or a plastic garbage bag) through the back of the seat strapping as shown in the photos. It can help to use a small pouch with a little weight to help hold the unit in place if using the original webbing carrier rack.
On my trip bike I use a rigid carrier rack. To give the “fender” some support and prevent it from sagging and touching the tire, I simply cut a piece of thin plywood such as 1/8″-3/16″ (available from hobby shops or woodworking supply stores) about 4″ wide and slide it inside the folder-over stuff bag or garbage bag.
