The platform part is likely a tall order for the built in water system when you code things up - in a fortnite setting its probably even worse.
Im not sure if it is possible, but one would likely need to extend the fortnite funcrionality to include the bouyancy points on models in order to create accurate platforms.
If you can figure out how to add bouyancy points and modify their values, you can likely create Ok working water floating platforms.