I posed the question about the concern I and others had about moisture getting into the airbox to Jeff, who runs a very comprehensive blog and posts all kinds of in depth test results about various mods (
http://mygolfmk7.com/).
Below is his reply for those that are interested:
“I'm skeptical that water entering the intake is an issue when opening that side. Since the opening sits above the hood line water would need to be traveling upward to get in. Then it has to turn downward to get into the airbox, and then it has to turn upward again to reach the air filter. Water droplets that would be able to remain in the air stream along that path would have to be small, small enough that they would also be able to enter from the passenger side.”