The interior PCA's can be conformal coated (if they're not already). The motors are three lead devices, no hall effect sensors or shaft encoders. Not much to the motors themselves. On my P4, with the props on, I can't see into the motors. Considering the simplicity of the motors themselves, and the care DJI took to protect the motors, they should hold up OK in moderate rain. The only thing I may worry about are the bearings (or whatever the motors use). You can always get a replacement motor and run it in distilled water. No kidding, that is what I would do. Then there's the camera/gimbal. The lens is protected by the skylight filter. The ribbon cable interconnects are another point of entry for moisture. Thick conformal coat (Humiseal) would probably seal up the ribbon cables. Then there's the gimbal motors themselves. They're brushless, but the possibility exists that the gimbal motors use some sort of encoder. I think this may be the case as gimbal positioning motors must position themselves much more precisely than the motors that spin the props (which don't have to position themselves at all), the processor would require more feedback than the back-emf three wire scheme that the prop motors use to send data to the processor. If the gimbal motors have more than three conductors running into them then there is some sort of encoder in there that may not take kindly to water. Perhaps you can construct some sort of skirt (or whatever) to protect the camera/gimbal assembly.
It's unlikely that there is an off the shelf solution available, at least nothing affordable. Keeping the bird stable in 15mph winds is possible. Keeping the bird stable with water pushing against it? Who knows?
FWIW, I've been thinking about flying the bird in the rain and snow.
Cheers
