I don't like the Munson plan. I personally feel its too aggressive and puts too much emphasis on weights or prey and snake.

If you can't see a lump, then move up in prey size. Then feed that size until you no longer see a lump after 24 hours. Then move up. Continue this process until you hit large mice, even if there's no lump, an adult corn doesn't need more than a large mouse. Feed your snake once a week doing this method, and you'll have a happy healthy snake.