Here is the formula I have been using for watermelon. Took me a while to get it the way I wanted even though it isn't real involved. I'm a bit of a perfectionist though

1/2 cup plastic
3 drops Green Pumpkin (Lurecraft)
1 drop watermelon (Lurecraft)
1 drop Natural (Lurecraft)
4 drops Lime green (Lurecraft)
Optional: 2-3 drops watermelon 101 (lureworks) if you feel like it needs just a little more watermelon vibe to it.