A brief lesson in building saddlebags from Army ammo boxes.
1) Buy Ammo boxes. Go to any military surplus store, they're around $6 to $10 apiece
2) Drill holes for mounting brackets, turn signals, turn signal wires. Drill the upper bracket holes, then fit the box to the bike. Then you'll be able to see where to drill the holes for the lower brackets.
These boxes are pretty tough, made of steel and have a nice, heavy rubber gasket in the lid that makes for a nice, tight seal. You can see a handle dangling down from the back of the box in some of the photos. That's for holding the box while opening it. I've added a strip of reflective tape to mine to increase visibility and maintain the black & white color scheme of the bike.