I got the idea for these Panniers from this Instructable https://www.instructables.com/id/Waterproof-Bicycle-Pannier-Boxes/ The dispensers I used are called Buddeez 4-Gallon Kingsford Kaddy.
I didn't want the 8 gallon dispensers because they would be too big for my Bike so I bought the 4 gallon ones from Tractor Supply. I happened to get them on sale for about $7 each. They go on sale from time to time so keep checking if you want a lower price. Even at the normal price they're fairly cheap.
The hooks on top are small but they fit well over the rails on my cargo rack. I slit some plastic tubing and slipped it over the rails, where the hooks go, to prevent scratching.
Photo #3 shows the hooks and springs I bought from Menard's. The springs are about 3 1/2" long and the loops on the ends are 5/16". They're fairly stiff springs. I used S hooks and 1/4" x 3/4" long bolts to attach them to the dispensers. I used 1/4" x 1" fender washers on the inside for reinforcement (photo #5). Since the holes on the hooks are close together, I had to use regular washers on the bolts. I used S hooks on the springs to connect them to the bike. I have 2 threaded holes on either side of my frame so the S hooks go in those. The spring on the inside hold the dispenser down and the springs on the bottom keep the dispenser from swinging out during cornering. I put some foam rubber in the bottom for cushioning.
I don't plan to carry anything heavy with these, maybe a few groceries.