I am not a watermelon person, but I got this from a friend. I have made this with other fruit like honey dew melons and cantaloupe, I will make those recipes too.... This is a favorite at our summer get-together..
Cut 1/2-inch thick slice from bottom of watermelon to prevent it from rolling around. Scoop watermelon in batches , in blender until smooth: pour each batch of juice into separate large bowl. (You should have about 7 cups of juice.)
Pour 2 cups of juice into saucepan: bring to boil. Remove from heat. Add dry gelatin mixes; stir 2 min. until completely dissolved. Add to remaining large bowl: mix well.
Refrigerate 45 min. or until thickened, stirring every 15 mins. pour into watermelon shell. Refrigerate 3 hours until firm. When gelatin is firm, cut away any watermelon rind that extends above gelatin layer.