I have played woodsball once and it poured rain in the middle of the game. I got soaked do did the marker and hopper.
Just wiped off the water and it was fine. Rain drops just fall off the outside.
If you were playing tourney and did a dive into a puddle and submerged the marker completely, then you may have water issues, like this --->>>> https://www.youtube.com/watch?v=XQbTHyv51E8#t=86