Flying the drone on the water can be stressful enough with out having to worry about your UAV getting wet.
I have owned the Phantom 1, 2, 3 and now the 4. Being on the water quite often my first purchase has usually been a waterproof case.
These drones has traveled with me all over. Arkansas, Texas, Louisiana, Bahamas, Mexico and as far away as Indonesia. I needed something tough, waterproof and travel well.
I have been using several versions of water proof cases since my Phantom 2 vision plus. My current favorite as been the case by Case Club. They are well thought out close cell foam cut out, waterproof, travels very well and has a life time warranty.
They sell for almost half the price of the other company at $169.00 on Amazon.com.
Here is a review of the product as I go step by step on the features I like. If you have a DJI phantom 4 and need something tough and waterproof you will be hard pressed to find anything of better value.