I've seen pictures of people putting swimming pool foam "noodles" on their landing gear secured with tie wraps. Not so much for water landings per SE, but at least it will float to aid in recovery. Even if it's upside down and the electronics get dunked, you should be able to salvage most of it. Put everything in a big bag of rice and keep it in a warm place for a week to 10 days). That has saved many a cell phone that went swimming. Figure out how much " noodle" It takes to float the equiv weight of the phantom.
I have so many lakes and retention ponds around me I've been tempted to do this for a while
