Preheat oven to 300° and spray a 13×9 with non-stick spray.
Drain and rinse the beans and dump them into a large bowl.
Add ketchup, brown sugar, mustard, bacon, and onion.
Stir until it is well combined and pour into prepared pan.
Cover with foil and cook 3 hours, removing foil for the last hour.
You can cook them up to 6 hours, just leave the foil on until the last hour.