This is the conformal coating that I've been using to protect my drones for over 4 years. My quads end up in the water nearly every week...and we flew through a bando in the rain yesterday...Wether you end up hitting a droplet of dew on a blade of grass or you sink your quad in the Abyss, Conformal Coating is the way to protect your electronics from water damage.
MG Chemicals is great for every board on your quad, but dont paint it in buttons, switches, or connectors that you plan to use.
422B - Silicone Modified Conformal Coating
422B is a 1-part, acrylic-silicone blend conformal coating that cures to a durable, flexible and smooth finish. It is easy to apply and can be handled in only 8 minutes. It may be removed with appropriate strippers, or soldered through for repair or rework.
422B is designed for applications where both high service temperature and flexibility are required. It puts minimum stress on components during thermal cycling, making it ideal for applications that involve a wide temperature range. It provides strong protection against moisture, corrosion, fungus, dirt, dust, thermal shock, short circuits, high-voltage arcing, and static discharge.