We did consider a wetsuit for the
P4P+ and Phantomrain was very honest when I asked a question (on the sister PhantomPilot forum) a few years back The only advantage in flying in the rain for us was if we could capture heavy rain falling, but the actual reality was that it wouldn't have worked on film using a drone even as good as the
P4P+. Filming in the rain using a drone is otherwise counterproductive because the light is obviously poor/bad under these conditions and this will be reflected in your video footage. Any photographer/filmmaker will tell you that "light is everything". You've also got to consider the controller getting wet, although an umbrella held by someone would partly solve that issue.
Do the wetsuits work? Whereas we have no experience, I've watched a few of Phantomrain's videos a while back and they seem to do so
As for landing on water - whether it be the sea or a lake - you have to consider wind and tide. Unless you have a boat, or wish to go swimming, your realistic chances of rescuing a drone lost at sea or on a lake aren't good. I know this for a fact on even a small lake with regards to other (not-a-drone) floating objects.