Dice and fry bacon until half done. Add chopped onion, cook until slightly browned, pour off most of the grease. Add pork and beans, brown sugar, vinegar, and catsup. Stir well, cover.
Bake the beans slowly in a 300 degree oven for a couple of hours. Or, if you prefer, you may simmer them very slowly on top of the stove for about 30 minutes.