I don't know if you're still working on this but, Flavorah Wild Melon starting at 0.15% will add juiciness. At higher % you get the melon. I'm one of those that can't taste strawberry so no help there. To boost the watermelon add another, like FW Candy Watermelon for a candy effect. Add anther cooling agent like ws-23. I would also lower the super sweet to 0.5%. It can mute flavors too, not to mention kill coils.