Fill a medium-size bowl with water, and add salt until water is heavily salted. Place seeds in the bowl, and let sit for 1 to 2 hours.
Preheat oven to 325°F. Line a baking sheet with parchment paper. Drain the seeds and place on a towel to pat dry; use the towel to remove any goo around the seeds, if possible.
If coconut oil is firm, place a tablespoon or two in the microwave for 10-30 seconds, until melted. Toss the seeds with coconut oil, adding a little bit at a time until the seeds are lightly coated. The more seeds you get from your watermelon, the more coconut oil you will need.
Scatter seeds in a single layer onto the baking sheet. Roast seeds for 25-35 minutes, until crisp, stirring after 15 minutes. Transfer to a paper towel and allow the seeds to cool completely before eating. To store, place seeds in a sealed container in the refrigerator.
NOTE - measurements are approximate, needed to put something in for posting purposes.